(The mistake becomes visible when you go to the end of a very long line
of double-width characters: the $ will be shown on the right edge, even
though you're already at line's end.)

This reverts commit 16a7fd4b from yesterday.

What is the point of parsing a number when you're not interested in
the result?  All callers of parse_num() pass a container for it.

This addresses part of https://savannah.gnu.org/patch/?9216

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

When there is no end match after a start, it is pointless to look
for any more starts because also they will not have any end match,
so nothing will get painted -- just cut the loop short.

This fixes https://savannah.gnu.org/bugs/?50009.

The renamed variable 'index' is not the start of a match (as some comment
mistakenly said), but from where in the line we start looking for a next
match.

Also, use one more goto to allow unindenting a big piece of code, and
shortcircuit two while loops for two more small unindents.

The setting of current_y in copy_from_filestruct() also appears to be
a holdover from the days of a more-common STATIONARY scrolling mode.

do_cut_text() uses the above function when copying text (uncutting
text again right after cutting it).  Since the text is effectively
the same afterward, current_y doesn't need to change.

do_uncut_text(), however, does need current_y up to date in one case:
when uncutting a full screen or less' worth of lines, focusing will be
FALSE, and it uses edit_refresh(), so it will use STATIONARY scrolling
mode then.  Take a cue from do_insertfile() and call reset_cursor() to
get an updated current_y.

(Note that the check for a full screen or less' worth of lines uses
incorrect values when in softwrap mode, but that's a separate problem.)

undo_cut(), do_redo(), and backup_lines() do not need set current_y
because they all result in edit_refresh() with focusing = TRUE, so
they do a CENTERING scroll which does ...

At first paintlen was computed as a column span, and then converted
to a character count...  Confusing.

The top_x variable has already been forced to become equal to from_x
if it was before it.  So start_col will be at least zero.

It is the misuse of "x_" to mean a column position on screen, and the
misuse of "_col" to mean a character position in a string that causes
this confusion.

All these different "start"s and "end"s are confusing.  Use instead
'from_x and 'till_x' to remember which part of the current line is
visible now on screen and is thus represented in 'converted'.

Also adjust a few comments.

In order to determine the correct multidata for a line that doesn't
have such data yet, the whole line must be examined, not just the
part that fits within the screen width.

This fixes https://savannah.gnu.org/bugs/?49978.

That is: only extend the current Del or Backspace undo item when the
cursor is still (or again) at the same spot.

This fixes https://savannah.gnu.org/bugs/?50006.

This fixes https://savannah.gnu.org/bugs/?49994

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

Instead of setting openfile->current_y (and wrongly so), just call
reset_cursor() to recompute current_y and place the cursor on that
line (if it is not offscreen).

The search routine begins searching right after the cursor and behaves
as if the line starts there, which means that a beginning-of-word anchor
(\< or \b) will match there also when in fact the cursor is sitting in
the middle of a word.  To prevent finding a false match, verify that
for a regex that starts with a BOW anchor the found match is actually
the start of a word.

This fixes https://savannah.gnu.org/bugs/?45630.

This fixes https://savannah.gnu.org/bugs/?49824.

Since do_mouse() uses edit_redraw(), openfile->current_y will be
immediately recalculated, so there's no point in changing it now.
Use a temporary variable instead.

The value of sameline doesn't change, so it can be initialized to that.

Since i holds openfile->current_y, it should be ssize_t, not size_t.

And it's better to do the most significant part of a calculation first.

The conditionalizing saved negligible amounts of space, of memory, and
of speed.

In that case setting the latter to TRUE is misleading.  So don't do that.

Many of the adjustments of the value of openfile->current_y appear to be
a holdover from the days when certain functions had to account for what
is now called STATIONARY scrolling mode, which depends on the value of
current_y.  Remove these adjustement where they are superfluous.

do_para_begin(), do_para_end(), and do_bracket_match() update the screen
through edit_redraw(), which uses either CENTERING or FLOWING scrolling
mode, so their setting of current_y is redundant and useless, as it will
be ignored and then overridden by the next call to reset_cursor().

findnextstr() is called by go_looking() [which calls edit_redraw(), see
above], and by do_replace_loop() and do_int_spell_fix(), which both call
edit_refresh(), which in this case only uses CENTERING scrolling mode
since focusing is TRUE.

(Additionally, the adjustments of current_y in findnextstr() and
do_bracket_match() use incorrect values when in softwrap mode.)

find_paragraph() doesn't need to save or restore current_y, because it
doesn't do any screen updates.  do_justify() calls edit_refresh() with
focusing set to TRUE, so it uses the CENTERING scrolling mode.

do_alt_speller() and do_formatter() do not need to save and restore
current_y, because they don't modify it in any way.

This addresses https://savannah.gnu.org/patch/?9197.