Since commit 8490f4ac, get_edge_and_target() depends on an up-to-date
current_x.  So: make sure current_x is updated when we move to the
top left of the screen to start a non-smooth PageUp or PageDown.

This fixes https://savannah.gnu.org/bugs/?51480.

For some reason, when returning from suspension, SLang will produce
either a clipped error code (0xFF instead of 0xFFFF, when returning
from an externally induced suspension), or it will clip the code of
first subsequent keystroke to a single byte (when returning from a
normal, in-editor suspension: ^Z).

Side-step this by ignoring the clipped error code, and by using an
undefined control code as the first fake keystroke.  Ignoring the
clipped error code is not possible when using a single-byte locale,
otherwise the user would not be able to type the character with
code 0xFF (although it could still be entered with Esc Esc 255).

This fixes https://savannah.gnu.org/bugs/?51477.

And reword them too, so that it is clearer what the mechanism is
for determining which syntax to use for a file.

Rename the corresponding rc-file option too, of course.

Color it bright green instead, like valid numeric arguments of
'fill' and 'tabsize'.  Also color the argument of 'formatter'.

And in the bargain improve some mark-up here and there.

And rewrap the feature toggles, so that a title does not start
a sentence.

And refer backward instead of forward.

I like it better that ^X stays in the same position compared to the
main screen: the lower left corner.

This fixes https://savannah.gnu.org/bugs/?51457.

The help lines need to be redrawn one step after a justification
(whether it has been undone or not, to replace "Unjustify" with
"Uncut" again for ^U), and after switching buffers (to update a
possibly changed tag for ^T).

This fixes https://savannah.gnu.org/bugs/?51455.

Make them reflect the split into two functions, the direct use of
tabsize, and the difference in behavior between indent and unindent.

Since all indentation and unindentation is by a tab, or by a tab's
worth of spaces, use tabsize directly.

Also remove one unneeded blank line.

The parameter 'cols', that indicates how many columns to indent or
unindent, is changed to be always positive, so the check for being
negative can go.  And it could never be zero anyway.

This is the first step toward splitting them into two dedicated
functions, instead of letting do_indent() handle both cases.

The precalculation of the multiline regexes no longer looks at the
keyboard every second, and the backup code makes use of futimens()
nowadays.

Well, it will compile even without that include.  :|
I don't know why, since it does use va_list.

When compiling with 'clang', it would say: warning: expression which
evaluates to zero treated as a null pointer constant of type 'char *'.

This fixes https://savannah.gnu.org/bugs/?51427.

In nano, -a is only effective when also -$ is given, so this will
not conflict with Pico since Pico does not know the -$ option.

This should eliminate all cases where the newline is pushed off the edge
of the screen in non-atblanks softwrap mode.  Also, it allows the use of
the last column of the screen in atblanks softwrap mode when a piece of
text does not contain any blanks.

This avoids the unreachable end-of-line reported on the mailing list:
http://lists.gnu.org/archive/html/nano-devel/2017-06/msg00011.html.

And then elide the function entirely as it's called just once.

Extend get_softwrap_breakpoint() to break softwrapped lines on
whitespace when a flag is set.  This flag is controlled by the new
rcfile option "atblanks".  The '>' characters marking two-column
characters at the edge of the screen are disabled when it's on.

If get_softwrap_breakpoint() can't find whitespace in screen range, it
will break the line on the screen edge.  (In this case, a blank can be
on the last column of the screen, but text can't, so that a blank on the
last column doesn't become invisible and possibly break the display.)

This fulfills https://savannah.gnu.org/bugs/index.php?49959

.
Requested-by: Nicholas Boel <axxisd@gmail.com>

spotlight() now displays softwrapped lines chunk by chunk instead of all
at once.  Since softwrapped lines are no longer of constant width, the
latter approach would fail if softwrapping breaks the spotlighted text.

Instead of taking a string, spotlight() now takes the starting and ending
columns of that string.  Also, its handling of softwrapped lines is now
split off into a separate function, spotlight_softwrapped().