regex: treat [x] as x if x is a unibyte encoding error Problem reported by Aharon Robbins in: http://lists.gnu.org/archive/html/bug-gnulib/2016-01/msg00091.html * lib/regcomp.c (parse_byte) [!_LIBC && RE_ENABLE_I18N]: New function. (build_range_exp) [!_LIBC && RE_ENABLE_I18N]: Use it.