Instead of inserting the extra whitespace after the current indentation
of a line, add it to the start of the line.  This causes a fixed amount
of visual whitespace to be added regardless of whether --tabstospaces
is used or not.

This fixes http://savannah.gnu.org/bugs/?51438,
and its ancestor https://savannah.gnu.org/bugs/?51408.

Without them, nano still compiles for me, with everything enabled,
even when using --enable-debug, --enable-utf8, and --with-slang.

Assume that a linter line that contains an actual error message or
warning includes a colon followed by a space -- something that that
opening message from a modern gcc lacks.

Human column numbers are one-based, whereas x positions are zero-based.
Converting from the one to the other involves subtracting one.  But when
the linter message does not provide a column number, the latter defaults
to zero.  Catch that case and change the number to one.

This fixes https://savannah.gnu.org/bugs/?51550.

The charalloc() macro does exactly this.

Commit 28beb3f9 added the 'forreal' parameter to prevent spotlight() from
placing the cursor wrongly due to an invalid placewewant.  However, since
the variable-width softwrap overhaul (specifically, since commit 8490f4ac),
place_the_cursor() no longer checks placewewant, so the parameter is no
longer needed.

Furthermore, dropping 'forreal' and thus always setting current_y won't
affect the operation of spotlight(), since the only functions that use
spotlight() (do_replace_loop() and do_int_spell_fix()) both call
edit_refresh() beforehand, which means that current_y will already
have been set to the value it will be set to again.

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.

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().

get_chunk_row() replaces the formula "column / editwincols".

get_chunk_leftedge() replaces "(column / editwincols) * editwincols".

get_last_chunk_row() replaces "strlenpt() / editwincols".

get_last_chunk_leftedge() replaces "(strlenpt() / editwincols) * editwincols".

This prepares us for any changes in those formulas, and for more such
functions later.

If the position of the cursor changes horizontally,
placewewant should change with it.

This fixes https://savannah.gnu.org/bugs/?51407

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

This matches the style in the rest of the code.

When blank_statusbar() has been called, make sure it is effective.

This fixes https://savannah.gnu.org/bugs/?51358.

(Well, redraw them when they're switched on, of course.)  Redraw
them so that they are shown correctly if their content changed.

This fixes https://savannah.gnu.org/bugs/?51356.
and fixes https://savannah.gnu.org/bugs/?51357.

When the active syntax contains a comment command that specifies the
empty string, this should override the default comment of "#" and
should disable the Meta-3 keystroke.

To achieve this, the comment string is now set by default to "#" for
all syntaxes, so that it will be set when no comment command is given
(including for the "none" syntax), and is unset only by explicitly
specifying «comment ""» in a syntax file.

This fixes https://savannah.gnu.org/bugs/?51355

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

And rename a third variable, to match another in its style.

Achieve this by making the suppression flag global, so that we can
just reset it instead of making an improper call of do_cursorpos().

This fixes the secondary part of https://savannah.gnu.org/bugs/?51134.

When spotlighting the string to be replaced, placewewant isn't valid,
so tell place_the_cursor() to ignore its value to avoid the cursor
getting mistakenly placed at the beginning of the next row.

This fixes https://savannah.gnu.org/bugs/?50997

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

And in the process transform the token DISABLE_HELP to ENABLE_HELP.

Call something a buffer when it refers to a linked list of linestructs,
and call something a linestruct when it is a struct that describes a
single line.

Also avoid an unused-variable warning, and trim a useless assert.