Call something a buffer when it refers to a linked list of linestructs,
and call something a linestruct when it is a struct that describes a
single line.

Also avoid an unused-variable warning, and trim a useless assert.

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

This fixes https://savannah.gnu.org/bugs/?47131.

When the user chooses not to open a file that some message refers to,
remove all messages for that file from the linting results, so the user
does not get asked about that same file again.

This fixes https://savannah.gnu.org/bugs/?47130.

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.

When Enter is pressed while the cursor is exactly on the current
indent width, remove the blank characters on that line to avoid
creating a line that consists only of trailing whitespace.

(When Enter is pressed somewhere in the middle of the blanks,
however, the whitespace is preserved.)
Suggested-by: Florian Zeitz <florob@babelmonkeys.de>

Verify at startup that the number is not too small.

Rename some variables in the process, and remove two cluttering asserts.

In do_int_spell_fix(), spell-checking text may change firstcolumn if
the next match is offscreen, and spell-checking text after that will
not change it back.  In order to keep the viewport unchanged, we have
to save and restore not just edittop, but firstcolumn as well.

In do_justify(), justifying text may change firstcolumn if the paragraph
ends offscreen, and unjustifying the text again will not change it back.
In order to keep the viewport unchanged, we have to save and restore not
just edittop, but firstcolumn as well.

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.

Most of these variables are freed moments later -- reallocating
them is thus a waste of time.

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

The mark only needs to be off when calling replace_marked_buffer(),
because this indirectly calls ingraft_buffer(), which fiddles with
the end points if the mark is on.

This fixes https://savannah.gnu.org/bugs/?50415.

Replace partitioning with calls to extract_buffer() and ingraft_buffer().

In addition to pasting the unjustified text back into the buffer at
current[current_x], ingraft_buffer() also deals with renumbering and
updating totsize, so do_justify() doesn't need to do those anymore
when unjustifying.

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.

In this last loop of break_line(), the pointer 'line' is one step ahead
of the index 'lastblank'.  So the loop should first add the length of
the preceding character to 'lastblank' before determining the length
of the current character (and using this to advance 'line').

(There is something wrong in the last loop: line is one character ahead
of lastblank, but the current character length is added to both of them.
It thus assumes that all blank characters are the same number of bytes.
For spaces and tabs this works fine.  But for more exotic blanks...)

Also, remove an assert and adjust some comments.

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.

This fixes https://savannah.gnu.org/bugs/?50379.

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

When the marked region covers only a single line (or a part of it),
its new endpoint is not simply the length of the last line of the
spell-checked text, but instead the old endpoint plus the /change/
in length.

This fixes https://savannah.gnu.org/bugs/?50316

.
Reported-by: David Lawrence Ramsey <pooka109@gmail.com>

If we're somewhere deep into the file and do a spell check, and the
first misspelled word happens to be right there, onscreen already,
then this word does not need to be centered -- it /should/ not be
centered.  We should scroll only when necessary.

Just like when spell-checking, there is no need to wrap around when
doing replacements in a region, because a region cannot straddle the
buffer's edges.

This is the proper fix for https://savannah.gnu.org/bugs/?50158,
and fixes https://savannah.gnu.org/bugs/?50273.

Make it clearer we're comparing the number of rows, not string lengths.

The spell fixer does not provide a beginning line, so the search routine
should then not try to refer to any data of this line.  Also, since the
changes to the search routine there is no need any more to retreat one
step before starting to search for a misspelled word.

This fixes https://savannah.gnu.org/bugs/?50159.

When the user answered No to a replacement prompt, skip the match
at the current position, so we don't stay stuck there.

Also, when replacing in the backward direction, or the match is
of length zero, skip the match at the current position, to not
get stuck.

This fixes https://savannah.gnu.org/bugs/?50126

.
Reported-by: David Lawrence Ramsey <pooka109@gmail.com>

This also fixes https://savannah.gnu.org/bugs/?50137,
and refixes https://savannah.gnu.org/bugs/?48635,
and fixes https://savannah.gnu.org/bugs/?50144.

That is: only extend the current Del or Backspace undo item when the
cursor is still (or again) at the same spot.

This fixes https://savannah.gnu.org/bugs/?50006.

The conditionalizing saved negligible amounts of space, of memory, and
of speed.