Original commit message from CVS: slurp in ffmpeg a) please test b) please help me figure out how to portably link in a .a file in our .so plugin
All aclocal .m4 files we need are put here and cat'd to acinclude.m4 in the source root. Official ones (taken from the relevant devel packages) are named as-is, unofficial ones (or changed ones) get a gst-prefix.