Original commit message from CVS: make ffmpeg erroring out work: - don't built gst-libs/ext/ffmpeg - don't update Tag when cvs command fails
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.