Require GNU m4 1.4 (well 1.3 in fact).
Because we are ready to handle the case where there are no frozen
files, we *have* to pass a -I, which is dangerous in conjunction
with the silent including of `aclocal.m4': you may include things
that were not expected. Since anyway handling pre 1.3 complicates
the task, just require an m4 which supports reloading of frozen
files.
* acspecific.m4 (AC_PROG_GNU_M4): Check for --reload.
* autoconf.sh: Likewise
* autoheader.sh: Likewise.
* configure.in: Explicitly state the m4 version you want.
