Prefer stoint to strtoul and variants

Prefer stoint to strtoul and variants

When parsing numbers prefer using strtosysint (renamed stoint)
to using strtoul and its variants.
This is simpler and faster and likely more reliable than
relying on quirks of the system strtoul etc,
and it standardizes how tar deals with parsing integers.
Among other things, the C standard and POSIX don’t specify
what strtol does to errno when conversions cannot be performed,
and it requires strtoul to support "-" before unsigned numbers.
* gnulib.modules (strtoimax, strtol, strtoumax, xstrtoimax):
Remove.
* src/checkpoint.c (checkpoint_compile_action, getwidth)
(format_checkpoint_string):
* src/incremen.c (read_incr_db_01, read_num)
* src/map.c (parse_id):
* src/misc.c (decode_timespec):
* src/sparse.c (decode_num):
* src/tar.c (parse_owner_group, parse_opt):
* src/transform.c (parse_transform_expr):
* src/xheader.c (decode_record, decode_signed_num)
(sparse_map_decoder):
Prefer stoint to strtol etc.
Don’t rely on errno == EINVAL as the standards don’t guarantee it.
* src/checkpoint.c (getwidth, format_checkpoint_string):
Check for invalid string suffix.
* src/checkpoint.c (getwidth):
Return intmax_t, not long.  All callers changed.
* src/incremen.c (read_directory_file):
It’s just a one-digit number, so just subtract '0'.
* src/map.c (parse_id): Return bool not int.  All callers changed.
* src/misc.c (stoint): Rename from strtosysint, and add
a bool * argument for reporting overflow.  All callers changed.
(decode_timespec): Simplify by using ckd_sub rather than
checking for overflow by hand.
* src/tar.c (incremental_level): Now signed char to
emphasize that it can be only -1, 0, 1.  All uses changed.
* src/xheader.c (decode_record): Avoid giant diagnostics.