(AC_PREREQ): Bump to 2.52.
(jm_AC_HEADER_INTTYPES_H): Remove; now done by autoconf in 2.52.
All uses removed.
(jm_AC_TYPE_INTMAX_T, jm_AC_TYPE_UINTMAX_T):
Move AC_REQUIRE to next-to-top level, to avoid confusion.
Use 2.52's AC_CHECK_TYPE instead of merely looking for the header.
Add AC_PREREQ(2.13).
(jm_AC_HEADER_INTTYPES_H): Test for intmax_t, too.
(jm_AC_TYPE_INTMAX_T): New macro.
(jm_AC_TYPE_UINTMAX_T): Moved here from uintmax_t.m4.