fixup: Automake installation works again

fixup: Automake installation works again

By renaming 'dist_automake_ac_DATA' to 'nobase_dist_automake_ac_DATA' in
a recent patch, we have broken the Automake installation, since m4 files
that were expected to be installed in '${prefix}/aclocal-${APIVERSION}'
are now being installed in '${prefix}/aclocal-${APIVERSION}/m4' instead.
Fix this mess.

* Makefile.am (nobase_dist_automake_ac_DATA): Rename ...
(dist_automake_ac_DATA): ... like this.  And move
'm4/internal/ac-config-macro-dirs.m4' ...
(dist_automake_internal_ac_DATA): ... here.
(automake_internal_acdir): New, simply defined to
'$(automake_acdir)/internal'.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>