This fixes https://savannah.gnu.org/bugs/?48622.

Achieve this by reusing the code that gives feedback when trying to
save a buffer while using --tempfile and the file has no name yet.

This fixes https://savannah.gnu.org/bugs/?48622.

Also for Delete, End, PageUp and PageDown (on some terminals)
the last byte in the sequence needs to be checked.

This fixes https://savannah.gnu.org/bugs/?49710.

Achieve this elegantly by factoring out the reading of one rcfile.

Also remove some unneeded prototypes, adjust some comments, and
move a constant definition to the top of the file.

Also improve or correct some comments.

If it would, the returned file descriptor would make nano crash,
because the corresponding stream has not been opened.  And when
returning zero instead (as the code did originally), nano would
open an empty buffer, although it claims to be reading the file.

In short: I think this is a leftover of an attempted fix of
https://savannah.gnu.org/bugs/?25297, from commit 2823c99e.

That is: when --rebindkeypad is in effect -- without this option
they were already getting distinguished.

Both would jump a word to the left -- now each jumps a word in the
proper direction.

This fixes https://savannah.gnu.org/bugs/?49636.

Kind-of-discovered-by: Markus Bergholz <markuman@gmail.com>

Also when somehow key_defined() is missing.

This fixes https://savannah.gnu.org/bugs/?49614

.
Reported-by: Mike Frysinger <vapier@gentoo.org>

(Bug was introduced yesterday, by commit a4132e2e.)

Otherwise the user can override a 'set nowrap' in /etc/nanorc only
via the command line.

This fixes https://savannah.gnu.org/bugs/?49593 reported by Shirish.

This fixes the two bugs reported by Anton Minaev
in https://savannah.gnu.org/bugs/?49511.

This fixes https://savannah.gnu.org/bugs/?49530.

Reported-by: Sumedh Pendurkar <sumedh.pendurkar@gmail.com>

This fixes https://savannah.gnu.org/bugs/?49467.

When giving a line number on the command line, do_gotolinecolumn() needs
to know the width of the screen to be able to (roughly) place the target
line in the center of the screen.

This fixes https://savannah.gnu.org/bugs/?49462.

This fixes https://savannah.gnu.org/bugs/?49423.

Also remove some cluttering conditional compilation.

Also, don't bother conditionalizing two booleans for the tiny version.

The nanorc option already exists, but not the corresponding one
for the command line.

This fixes https://savannah.gnu.org/bugs/?49428.

This make tiny nano slightly less tiny, but makes the code more readable.

It does not update anything -- it just picks a new point from
where to start displaying the buffer.  All actual updating of
the screen is done by edit_refresh() and edit_redraw() and such.

This fixes https://savannah.gnu.org/bugs/?49406.

There is no need to look at this for every painted line, because
the margin can only change when some key is struck.