maint: remove need for mbsalign

This simplifies memory allocation a bit, and removes an arbitrary
limitation from numfmt, which formerly limited cell output to 127
bytes.
* bootstrap.conf (gnulib_modules): Remove mbsalign, strncat.
Add strnlen (the code already used strnlen directly, and we were
saved only because Gnulib used the module indirectly)
* gl/lib/mbsalign.c, gl/lib/mbsalign.h, gl/modules/mbsalign:
* gl/modules/mbsalign-tests, gl/tests/test-mbsalign.c: Remove.
* src/df.c, src/ls.c: Do not include mbsalign.h.
(MBSWIDTH_FLAGS): New constant, now used for all
mbswidth calls.  All callers changed to check for -1 return.
* src/df.c (struct field_data_t): ‘width’ is now int not size_t,
since mbswidth can’t do widths greater than INT_MAX anyway.
Replace ‘align’ with ‘align_right’.  All uses changed.
(print_table): Redo to avoid the need for ambsalign.
(get_header, get_dev): mbswidth returns int, not size_t.
* src/ls.c (MAX_MON_WIDTH): Remove; no longer used.
(abmon_init): Use strnlen to cheaply discard too-long month names.
Align by hand instead of using mbsalign.
* src/numfmt.c: Include stdckdint.h, mbswidth.h.
Do not include mbsalign.h.
(padding_buffer_size): Now idx_t.  All uses changed.
(padding_width): Now intmax_t, since it’s no longer an object
size.  Its sign now records alignment.  All uses changed.
(zero_padding_width): Now int, since it’s given to sprintf.
All uses changed.
(padding_alignment): Remove; it’s now taken from padding_width’s sign.
(double_to_human): Return string length.  BUF_SIZE arg is now idx_t.
Include suffix in output.  All callers changed.  Simplify by not
calling strncat or stpcpy.  Calculate fmt size bound more carefully.
(setup_padding_buffer): Remove.  All uses removed.
(parse_format_string): Use intmax_t, not long, for pad.
On overflow, set widths to large values that cause later code
to do the right thing, rather than separately checking for
overflow here.
(prepare_padded_number): Return bool, not int 0/1.  New arg
PADDING.  All uses changed.  Do not limit padded output to 127
bytes; instead, use xpalloc to expand the output buffer.
(print_padded_number): New arg PADDING.  All uses changed.
(process_suffixed_number): Simplify.
(main): Take extremum if xstrtoimax overflows, as this does
the right thing.
* tests/misc/numfmt.pl: New test suf-20 to test for truncation bug.
Remove tests pad-3.2, fmt-err-7, as they’re no longer invalid but
are quite expensive.

bootstrap.conf

@@ -169,7 +169,6 @@ gnulib_modules="
   manywarnings
   mbrlen
   mbrtowc
-  mbsalign
   mbschr
   mbslen
   mbswidth
@@ -259,7 +258,7 @@ gnulib_modules="
   stpcpy
   stpncpy
   strdup-posix
-  strncat
+  strnlen
   strnumcmp
   strsignal
   strtoimax