join,uniq: support multi-byte separators

join,uniq: support multi-byte separators

* NEWS: Mention this.
* bootstrap.conf (gnulib_modules): Remove cu-ctype, as this module
is now more trouble than it’s worth.  All uses removed.
Add skipchars.
* gl/lib/cu-ctype.c, gl/lib/cu-ctype.h, gl/modules/cu-ctype:
Remove.
* gl/lib/skipchars.c, gl/lib/skipchars.h, gl/modules/skipchars:
* tests/misc/join-utf8.sh:
New files.
* src/join.c: Include skipchars.h and mcel.h instead of cu-ctype.h.
(tab): Now mcel_t, not int.  All uses changed.
(output_separator, output_seplen): New static vars.
(eq_tab, newline_or_blank, comma_or_blank): New functions.
(xfields, prfields, prjoin, add_field_list, main):
Support multi-byte characters.
* src/numfmt.c: Include ctype.h, skipchars.h.
Do not include cu-ctype.h.
(newline_or_blank): New function.
(next_field): Support multi-byte characters.
* src/sort.c: Include ctype.h instead of cu-ctype.h.
(inittables): Open-code field_sep since it no longer exists.
‘sort’ is not multi-byte safe yet, but when it is this code
will need revamping anyway.
* src/uniq.c: Include mcel.h and skipchars.h instead of cu-ctype.h.
(newline_or_blank): New function.
(find_field): Support multi-byte characters.
* tests/local.mk (all_tests): Add tests/misc/join-utf8.sh