ext/ogg/: Fix memleak in oggdemux when running unconnected pads. doc update in mux, start working on keyframe mode.

Original commit message from CVS:
* ext/ogg/gstoggdemux.c: (gst_ogg_pad_push):
* ext/ogg/gstoggmux.c:
Fix memleak in oggdemux when running unconnected pads.
doc update in mux, start working on keyframe mode.