More `unsigned char' -> `re_char' changes.

More `unsigned char' -> `re_char' changes.
Also change several `int' into `re_wchar_t'.
(PATTERN_STACK_EMPTY, PUSH_PATTERN_OP, POP_PATTERN_OP): Remove.
(PUSH_FAILURE_POINTER): Don't cast any more.
(POP_FAILURE_REG_OR_COUNT): Remove the cast that strips `const'.
We want GCC to complain, since this piece of code makes
re_match non-reentrant, which *should* be fixed.
(GET_BUFFER_SPACE): Use size_t rather than unsigned long.
(EXTEND_BUFFER): Use RETALLOC.
(SET_LIST_BIT): Don't cast.
(re_wchar_t): New type.
(re_iswctype, re_wctype_to_bit): Make it crystal clear to GCC
that those two functions will always properly return.
(IMMEDIATE_QUIT_CHECK): Cast to void.
(analyse_first): Use recursion rather than an explicit stack.
(re_compile_fastmap): Can't fail anymore.
(re_search_2): Don't check re_compile_fastmap for failure.
(PUSH_NUMBER): Renamed from PUSH_FAILURE_COUNT.
Now also sets the new value (passed in a new argument).
(re_match_2_internal): Use it.
Also, use a new var `reg' of type size_t when looping through regs
rather than reuse the inappropriate `mcnt'.