(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.