* character.c (Fchar_width, c_string_width, lisp_string_width):
* character.h (CHAR_WIDTH):
* indent.c (MULTIBYTE_BYTES_WIDTH):
Use sanitize_char_width to avoid undefined and/or bad behavior
with outlandish widths.
* character.h (sanitize_tab_width): Renamed from sanitize_width,
now that we have two such functions.  All uses changed.
(sanitize_char_width): New inline function.

* character.h (sanitize_width): New inline function.
(SANE_TAB_WIDTH): New macro.
(ASCII_CHAR_WIDTH): Use it.
* indent.c (sane_tab_width): Remove.  All uses replaced by
SANE_TAB_WIDTH (current_buffer).
* xdisp.c (init_iterator): Use SANE_TAB_WIDTH.

* fontset.c, lisp.h, xdisp.c: All uses changed.

Otherwise, CHAR_STRING would do the wrong thing on a 64-bit platform,
by silently ignoring the top 32 bits, allowing some values
that were far too large to be valid characters.
* character.h: Include <verify.h>.
(CHAR_STRING, CHAR_STRING_ADVANCE): Verify that the character
arguments are no wider than unsigned, as a compile-time check
to prevent future regressions in this area.
* data.c (Faset):
* editfns.c (Fchar_to_string, general_insert_function, Finsert_char):
(Fsubst_char_in_region):
* fns.c (concat):
* xdisp.c (decode_mode_spec_coding):
Adjust to CHAR_STRING's new requirement.
* editfns.c (Finsert_char, Fsubst_char_in_region):
* fns.c (concat): Check that character args are actually
characters.  Without this test, these functions did the wrong
thing with wildly out-of-range values on 64-bit hosts.

This fixes comparison bugs on 64-bit hosts.
(ASCII_CHAR_P): Use it.
* casefiddle.c (casify_object):
* character.h (ASCII_BYTE_P, CHAR_VALID_P):
(SINGLE_BYTE_CHAR_P, CHAR_STRING):
* composite.h (COMPOSITION_ENCODE_RULE_VALID):
* dispextern.h (FACE_FROM_ID):
* keyboard.c (read_char): Use UNSIGNED_CMP.