This avoids eleven warnings of the kind "comparison between signed
and unsigned integer expressions [-Wsign-compare]".

When the file has just been read, it is in the state that it has
on disk, so there is nothing to undo.

This fixes https://savannah.gnu.org/bugs/?53387.

That is, call display_string() just on the filename, not on the rest
of the prompt text.

This fixes https://savannah.gnu.org/bugs/?52967

.
Reported-by: Andreas Schamanek <schamane@fam.tuwien.ac.at>

And one for me, for the much changed keyboard stuff.

This fixes https://savannah.gnu.org/bugs/?52896

.
Reported-by: Miki Strange <mik@mikistrange.com>
Tested-by: Miki Strange <mik@mikistrange.com>

Each leading tab is converted to two tabs, and any leading four spaces
is converted to one tab.  The intended tab size (for keeping most lines
within 80 columns) is now four.

This fixes https://savannah.gnu.org/bugs/?52755

.
Reported-by: Brand Huntsman <alpha@qzx.com>

Unset the "Modified" marker only at the point where the file was last
saved -- if there is such a point, because it can be missing when the
undo stack was discarded.

This fixes https://savannah.gnu.org/bugs/?52689

.
Reported-by: Liu Hao <lh_mouse@126.com>
Original-idea-by: Brand Huntsman <alpha@qzx.com>

When doing that, there is no need to save and restore the Modified
state when writing a marked region.

To get rid of two double negatives.

This fixes https://savannah.gnu.org/bugs/?52519.

This also means that no question needs to be asked when exiting.

This fixes https://savannah.gnu.org/bugs/?52504

.
Reported-by: Peter Passchier <peter@passchier.net>

Otherwise we would overwrite the current file with just the selection.

This fixes https://savannah.gnu.org/bugs/?52482.

The pointer not being NULL is enough indication that the mark is set.

Also, rename the pointer from 'mark_begin' to simply 'mark', since
the former is kind of pleonastic.

While doing that, move the affected function to the utils.c file
and tweak it a bit.

This fixes https://savannah.gnu.org/bugs/?52468.

This fixes https://savannah.gnu.org/bugs/?52392.

Also, properly refer to numreplaced as signed, since it's ssize_t
(even though it's only shown when positive).

In the tiny version, do_prompt() will now have an extra NULL
parameter, which will cost maybe twenty extra bytes of code.
That is acceptable when it saves thirty lines in the source.

The key sequence ^R ^X M-F <Enter> would cause nano to abort, because
it would try to add an empty string to a history list.  (Furthermore,
simply don't execute an empty command, because it is pointless.)
Reported-by: Marco Diego Aurélio Mesquita <marcodiegomesquita@gmail.com>

^S will be the first thing people will try for saving a file,
and ^Q is somewhat mnemonic because it is to the left of ^W:
it searches backward.

Make these keystrokes available also in the tiny version.