do CVS surgery and related build fixery to move elements and indexers in a new gstreamer/plugins directory, out of th...

Original commit message from CVS:

* Makefile.am:
* configure.ac:
* plugins/elements/Makefile.am:
* plugins/elements/gstcapsfilter.c:
* plugins/elements/gstfilesink.c:
* plugins/elements/gstfilesrc.c:
* plugins/elements/gstidentity.c:
* plugins/indexers/Makefile.am:
do CVS surgery and related build fixery to move elements
and indexers in a new gstreamer/plugins directory, out of the
gst/ directory