When the editing space gets narrower, either by toggling line numbers on
or making nano's window smaller, and when the cursor is near the bottom,
it can be pushed offscreen.  In that case, don't get it back onscreen by
centering the current line but by putting it on the bottom row.  This
makes for a smoother experience.

This fixes http://savannah.gnu.org/bugs/?50933.

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

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

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.

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.

The mbwidth() function itself checks whether UTF-8 is being used
and does the right thing.

Also, mention that help texts can now be searched through, update
a copyright notice, and update and simplify a copyright year.

And in the process transform the token DISABLE_HELP to ENABLE_HELP.

The top-left corner changing is far more conspicuous than the top right.

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>

This fixes https://savannah.gnu.org/bugs/?50872.

The go_back_chunks() function will do this clipping.

This fixes https://savannah.gnu.org/bugs/?50866.

It takes almost no code and is a useful little improvement over Pico.

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

To avoid an ncurses hiccup (miscoloring) when running on musl.

This fixes https://savannah.gnu.org/bugs/?50787

.
Reported-by: Avi Halachmi <avihpit@yahoo.com>

The cursor needs to be placed in its proper spot in the edit window
/only/ when nano is about to accept input from the user and needs to
show where this input will go.

(This might cause a scrolling issue to appear, because reset_cursor()
does not just place the cursor, it also recomputes current_y, which
is used in several places to determine whether and how much to scroll.
If it so happens, we'll deal with that fallout later.)

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.

Make nano recognize the escape sequences for Ctrl-Home, Ctrl-End,
Shift-Ctrl-Home, and Shift-Ctrl-End on xterm, rxvt, and Eterm.

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.

When a multi-column character straddles a chunk boundary, and the
preferred column (placewewant) for the cursor is zero, cheat: show
the cursor not where the character starts but on the beginning of
the next row.  This makes the cursor move smoothly in the leftmost
column of the screen when using <Up> and <Down> and such, instead
of jumping around.

In this way the scrolling logic won't get confused and the screen
will scroll properly when stepping beyond the top or bottom row.

This fixes https://savannah.gnu.org/bugs/?50687.

This fixes https://savannah.gnu.org/bugs/?50741.

Verify at startup that the number is not too small.

If edittop is partially offscreen before we scroll, and it gets
scrolled more offscreen, we do need to compensate for the chunks
between firstcolumn and leftedge -- that is: the chunks between
the top row and the cursor row.

This fixes https://savannah.gnu.org/bugs/?50691.

When a two-column character cannot be shown because it straddles the
boundary between two chunks of a line, show the '>' placeholder for
its left "half", and '<' for its right "half".

This mitigates https://savannah.gnu.org/bugs/?49440.

The leftedge variable is a column number, not an x position.

The number of rows to draw shouldn't be compensated for the chunks
of edittop that are before firstcolumn, because they are offscreen.

This completes the fix for https://savannah.gnu.org/bugs/?50621.

There is no need to always increase nrows by 1 or 2 -- an increase
of 1 is only needed when the line that borders on the scrolled region
needs to redrawn too: when this line was horizontally scrolled or when
the mark is on.

This fixes https://savannah.gnu.org/bugs/?50621

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

But apparently none of these cases occur, because I can't trigger them.

This could happen when a tab or a double-width character straddles
the boundary between two softwrapped chunks.