* alloc.c: Catch some string size overflows that we were missing.

* alloc.c: Catch some string size overflows that we were missing.

(XMALLOC_OVERRUN_CHECK_SIZE) [!XMALLOC_OVERRUN_CHECK]: Define to 0,
for convenience in STRING_BYTES_MAX.
(STRING_BYTES_MAX): New macro, superseding the old one in lisp.h.
The definition here is exact; the one in lisp.h was approximate.
(allocate_string_data): Check for string overflow.  This catches
some instances we weren't catching before.  Also, it catches
size_t overflow on (unusual) hosts where SIZE_MAX <= min
(PTRDIFF_MAX, MOST_POSITIVE_FIXNUM), e.g., when size_t is 32 bits
and ptrdiff_t and EMACS_INT are both 64 bits.
* character.c, coding.c, doprnt.c, editfns.c, eval.c:
All uses of STRING_BYTES_MAX replaced by STRING_BYTES_BOUND.
* lisp.h (STRING_BYTES_BOUND): Renamed from STRING_BYTES_MAX.