ext/ogg/gstogg.c: we require bytestream now

ext/ogg/gstogg.c: we require bytestream now

Original commit message from CVS:
* ext/ogg/gstogg.c: (plugin_init):
we require bytestream now
* ext/ogg/gstoggdemux.c:
huge diff to implement chain setup in a fast and generic way. This
improves tag reading and startup of huge files (read: Theora videos)
quite a bit. It probably contains bugs, too, so please test.
Seeking is not improved to the fast method.