gst/asfdemux/: Add tagging support to demuxer, split out registration in its own and prevent having some tables in ou...

Original commit message from CVS:
* gst/asfdemux/Makefile.am:
* gst/asfdemux/asfheaders.c:
* gst/asfdemux/asfheaders.h:
* gst/asfdemux/gstasf.c: (plugin_init):
* gst/asfdemux/gstasfdemux.c: (gst_asf_demux_get_type),
(gst_asf_demux_base_init), (gst_asf_demux_process_comment),
(gst_asf_demux_setup_pad):
* gst/asfdemux/gstasfdemux.h:
* gst/asfdemux/gstasfmux.c:
* gst/asfdemux/gstasfmux.h:
Add tagging support to demuxer, split out registration in its own
file instead of in demux (hacky), and prevent having some tables
in our memory multiple times (in asfheaders.h).