* src/arscan.c (parse_int): Fix integer overflow test

* src/arscan.c (parse_int): Fix integer overflow test

Use intprops.h macros rather than trying to detect integer overflow by
hand, and doing it incorrectly.  Example of incorrect behavior:
if val == 3689348814741910323, base == 10, UINTMAX_WIDTH == 64, and
 *ptr == '0' then (val*base)+(*ptr-'0') yields 18446744073709551614
which is greater than val even though overflow has occurred.
Fortunately this bug could not be triggered on GNU/Linux hosts,
although it may be possible on platforms (if any) where struct ar_hdr
has members so large that they can represent integers that do not fit
int uintmax_t.