Instead of allocating enough space to convert the entire passed string,
just allocate space for converting the part that will be converted --
that is: starting from start_index.  This still allocates far too much
(if the passed string is very long and its tail part won't fit on the
screen), but it's better than before.

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

Cap the number of pauses when displaying ALERT messages, to avoid
making the user wait for ages when tens or hundreds of files were
specified on the command line.

This fixes https://savannah.gnu.org/bugs/?50362

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

Reflect the significant changes in painting and regex searching
in the copyright notices.

Later on we're going to need the ability to graft a buffer into the
current file buffer without making a copy of it first.

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

When in softwrap mode, no "$" continuation characters are displayed,
so the code that reserves space for them should be skipped then.

This fixes https://savannah.gnu.org/bugs/?50335.

As a small service to the user, reject empty regex strings,
because an entirely empty regex simply doesn't make sense.
Inspired-by: Elia Geretto <elia.f.geretto@gmail.com>

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>

The inversion of the logic in commit a6605dce was incomplete -- oops.

This fixes https://savannah.gnu.org/bugs/?50306.

The previous code only directly refreshed the screen when the margin
changed due to toggling line numbering on.  When the margin changed
due to toggling it off, it would indirectly refresh via do_toggle().

When replacements are made, nothing needs to be reset any more
(it was done insufficiently anyway).  Just make sure the screen
is refreshed when all is done -- this may be superfluous when
doing interactive replacements, but not when replacing all.

The lines that come after an unpaired start have to know about this.

This fixes https://savannah.gnu.org/bugs/?50293.

When coloring a line, look only at the multidata of the preceding
line, and based on that determine what to seek in the current line.

This fixes https://savannah.gnu.org/bugs/?50292.

When painting a line, the multidata of the line /before/ it is valid
in most cases: it was determined just a moment ago.  And it tells us
all we need to know: whether there is an unpaired start match before
the current line or not.

The only exception is when painting the first line of the screen:
the multidata of the line before it might be stale.  So for the
first screen line we will always have to do some backtracking.
But that is left for later.

This fixes https://savannah.gnu.org/bugs/?50121.

Also, add two cross references: one in words, and one with a link.

Also, remove the special "+line,column" argument from among the options,
since it isn't an option -- put it in a separate paragraph instead.

These two functions unnecessarily copy make_new_node(); use that instead.

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.

Scrolling works on rows, not on lines.  Accordingly, rename the nlines
variable to nrows.  And rows should be of the type int, not ssize_t.

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