Standardize all include headers with their absolute paths within the AvxSynth source tree. There are only two exceptions to this:

Installed headers, which refer to each other locally, since
they all get installed to <>/avxsynth/

Headers which do not exist in the source tree. These were left alone,
but now have comments disclaiming the fact that they don't exist
in the tree. This makes it easy to find them. In the event that
these functions/headers ever do need to be brought back, then they'll
need to be properly adjusted for the absolute path convention of
the other headers.
Synchronize avxffms2 with upstream r753

Removes the postproc dependency from avxffms2, as this causes
builds of FFMS2 since last September (when postproc support was
completely purged from FFMS2) to work with avxffms2 at all.

FFMS2 2.17 still works, as the postproc dependency doesn't seem
to have been necessary for it in the first place.
Further reduce the absolute header paths to relative forms within the subprojects.
Remove ErrorHandlingExternal extension.
Since the VfW interface was removed, this no longer serves a purpose.
Merge pull request #97 from qyot27/avxffms2_sync

Synchronize avxffms2 with upstream r753
Merge branch 'headerfix' of git://github.com/qyot27/avxsynth into qyot27-headerfix

Conflicts:
	plugins/avxffms2/src/ffpp_avx.h
Update automake files to reflect include path simplification.