Merge some changes from GNU libc. Add prototypes.

Merge some changes from GNU libc.  Add prototypes.
(bcopy, bcmp, REGEX_REALLOCATE, re_match_2_internal):
Use memcmp and memcpy instead of bcopy and bcmp.
(init_syntax_once): Use ISALNUM.
(PUSH_FAILURE_POINT, re_match_2_internal): Remove failure_id.
(REG_UNSET_VALUE): Remove.  Use NULL instead.
(REG_UNSET, re_match_2_internal): Use NULL.
(SET_HIGH_BOUND, MOVE_BUFFER_POINTER, ELSE_EXTEND_BUFFER_HIGH_BOUND):
New macros.
(EXTEND_BUFFER): Use them (to work with BOUNDED_POINTERS).
(GET_UNSIGNED_NUMBER): Don't use ISDIGIT.
(regex_compile): In handle_interval, return an error rather than try to
unfetch the interval if we can't find the closing brace.
Obey the RE_NO_GNU_OPS syntax bit.
(TOLOWER): New macro.
(regcomp): Use it.
(regexec): Allocate regs.start and regs.end as one block.