Also, trim some comments and avoid an unused-variable warning.

Also, reshuffle two initializations to go sit with the other ones.

Things have morphed over time and display_buffer() no longer actually
displays the buffer -- it just displays the title bar, precalculates
the multiline color info, and schedules a refresh of the edit window.

This avoids https://savannah.gnu.org/bugs/?49912 while at the same time
avoiding to draw the edit window twice in a row -- the first drawing
would use a wrong margin, which results in a visible and irritating
shift left or right of the content upon the second drawing.

This fixes https://savannah.gnu.org/bugs/?50877.

And one-letter variables I cannot "see" -- they are too small.

An iterator should not be called "start_col", because it is only the
starting column at the very beginning.

Also, start_col (after the rename) can never be /larger/ than column.

And in the process transform the token DISABLE_HELP to ENABLE_HELP.

Allow the user to search in a help text with ^W and M-W.

Achieve this by not writing the help text directly to the screen
but first writing it to a temporary file and then opening this file
in a new buffer, and treating it specially: the normal file-reading
feedback is suppressed, the titlebar shows the headline of the text,
the cursor is hidden, and the menu is limited to just the up and down
movements and searching.

This fulfills https://savannah.gnu.org/bugs/?28994

.
Signed-off-by: Rishabh Dave <rishabhddave@gmail.com>

Because nothing gets reset to zero or to some initial value.

These functions are used only in the file in which they are declared,
and they are declared before they are used.

The interval 2013-2017 for the Free Software Foundation is valid
because in those years there were releases with changes by either
Chris or David, and the GNU maintainers guide advises to mention
a new year in all files of a package, not just in the ones that
actually changed, and be done with it for the rest of the year.

On some terminal emulators, Ctrl+Home and Ctrl+End produce special
keycodes, distinct from plain Home and End.  Make the users of those
emulators (and of the Linux console) glad by making ^Home and ^End
do the obvious thing, and the combinations with Shift too.

Verify at startup that the number is not too small.

Use futimens() instead of utime() to change the timestamps on a backup
file.  Otherwise, a non-privileged user could create an arbitrary symlink
with the name of the backup file and in this way fool a privileged user
to call utime() on the attacker-chosen file.

Import the relevant gnulib module to make sure futimens() is available.

If the number of columns in the edit window changes (which currently
only happens in two places: in regenerate_screen(), called when the
window is resized; and in main(), when line numbering mode is toggled),
the display will break if we're in softwrap mode and firstcolumn is
nonzero.  This is because the column width of softwrapped chunks has
changed, and firstcolumn is no longer the starting column of a chunk,
an assumption that all code using firstcolumn relies on.

To fix this problem, add a new function, ensure_firstcolumn_is_aligned(),
to adjust firstcolumn to the starting column of the chunk it's on, and
use it when the number of columns in the edit window changes.

(Note that this function uses the simplest possible fix, and could
probably be made more sophisticated.)

The new function, update_softwrapped_line(), is called from inside
update_line() when softwrap mode is on, so that existing calls remain
unchanged.  It takes no index, instead displaying edittop from column
firstcolumn, and all other lines from column zero.

If current is on edittop, it's displayed using the edittop rules, but
this is not a problem: if current[current_x] is above edittop at column
firstcolumn, it's offscreen, and that should be handled before calling
update_line() anyway.

Together with the preceding bunch of changes,
this fixes https://savannah.gnu.org/bugs/?47667.

Since all lines can be partially scrolled off the screen now
(except for the top line of the edit window, which is forthcoming),
ensure_line_is_visible() is no longer needed.

Since all lines can be partially scrolled off the screen now
(except for edittop, which is forthcoming), the maxlines global
variable and its computation mechanism are no longer needed.

Add the parameter be_clever to both functions.  When be_clever is FALSE,
smart home and dynamic home are disabled in do_home(), and dynamic end is
disabled in do_end(), so that these functions only move to the beginning
or end of the current line or chunk.

This simple home and end functionality is needed to improve do_left()
and do_right()'s horizontal behavior with softwrapped chunks, which is
forthcoming.

These improvements will eventually make do_home() and do_end() take
parameters.  Since the global function lists can hold only functions
without parameters, preemptively add do_home_void() and do_end_void(),
and make the global function lists use them.

The old name made it sound as if it didn't apply in softwrap mode.  But
it does: in softwrap mode a line needs updating  when the mark is on.

Add the new functions current_is_above_screen() (which doesn't account
for softwrapped chunks yet, but will when we can scroll edittop partially
off the screen, which is forthcoming), current_is_below_screen() (which
determines whether current[current_x] is past the softwrapped chunk at
the bottom of the screen), and current_is_offscreen() (the union of the
previous two functions).

edit_redraw() and edit_refresh() now use current_is_offscreen() to check
whether they should adjust the viewport, and adjust_viewport() now uses
current_is_above_screen() to determine whether current is on or below
the screen in FLOWING mode.

Add the new function less_than_a_screenful() to accomplish this.
It uses go_back_chunks() to count the number of softwrapped chunks
between the end point and the starting point of the paste.

Now softwrap mode and non-softwrap mode behave the same way when
uncutting fewer than editwinrows rows of text.  Accordingly, remove
the call to ensure_line_is_visible(), as it no longer applies.

These functions, go_back_chunks() and go_forward_chunks(), take a number
of softwrapped chunks (screen rows) to move, a pointer to a buffer, and
a location (specifically, a starting column of a softwrapped chunk).  If
they move successfully, they will update the buffer pointer and location
to point to the beginning of the softwrapped chunk they moved to.

Since non-softwrap mode is effectively just a subset of softwrap mode
in which every line takes up one chunk, these functions also work in
non-softwrap mode.  In this case, their starting column will always be
zero, as it would be in softwrap mode on a line that takes up one chunk.

Nothing uses these functions yet, but that is forthcoming.

Now that we pull in the gnulib getopt-gnu module, we can assume it exists.

Now that we pull in the gnulib regex module, we can assume it exists.

Switch over to gnulib for these.

Switch over to gnulib for these.

These are provided by gnulib now.

With read_file() revamped, it now uses partition_filestruct() indirectly
via ingraft_buffer(), so we can't use partition_filestruct() to replace
marked text in the alternate spell checker anymore without segfaulting.

Add the new function replace_marked_buffer() to accomplish this instead.
Based on replace_buffer(), it uses extract_buffer() to throw away the
marked un-spell-checked text, and then uses read_file() to insert the
spell-checked text at the position where the mark was.

Accordingly, remove unneeded partitioning and related stuff from
do_alt_speller().  Besides pasting the file into the buffer at
current[current_x], ingraft_buffer() also deals with renumbering,
updating totsize, and handling a magicline, so do_alt_speller()
doesn't need to do those anymore.

Move buffer handling and '\r' stripping from read_line() to read_file(),
so that the file gets its format determined and gets stored in its own
buffer entirely in one function.  Then use ingraft_buffer() to insert
this new buffer into the current one.

In addition to pasting the file at current[current_x], ingraft_buffer()
also deals with renumbering, the updating of totsize, and the handling
of a magicline, so read_file() doesn't need to do those anymore.

Note that all this makes read_file() depend on the position of
current[current_x] to know where to insert the file.  Accordingly,
set current_x to zero in initialize_buffer_text() instead of in
make_new_buffer(), so that replace_buffer() keeps working properly.

Also, rename a parameter to be less cryptic, and remove an entire
condition because the relevant block will never be reached when
getting called from the help routines: if blank_loc is negative,
the function will have bailed out in the preceding if.

Later on we're going to need the ability to graft a buffer into the
current file buffer without making a copy of it first.

The name "filestruct" was a mistake.  What was meant was:
buffer -- a linked list of structs that each describe a line.