m4: Reintroduce ax_is_release.m4.
m4: Reintroduce ax_is_release.m4.

Some Linux distrubutions ship an older version the GNU Autoconf
Archive that contains a buggy AX_IS_RELEASE macro that references a
non-existent $top_srcdir variable when checking for a git directory.
Store the our own copy of the latest ax_is_release.m4 macro file to
work around this issue.

ossama-othman/MaRC,ossama-othman/MaRC,ossama-othman/MaRC