Original commit message from CVS:
* ext/theora/theoradec.c: (gst_theora_dec_reset),
(theora_dec_push_forward), (theora_dec_push_reverse),
(theora_handle_data_packet), (theora_dec_decode_buffer),
(theora_dec_flush_decode), (theora_dec_chain_reverse),
(theora_dec_chain_forward), (theora_dec_chain):
Implement reverse playback.
* ext/vorbis/vorbisdec.c: (gst_vorbis_dec_reset),
(vorbis_dec_decode_buffer), (vorbis_dec_flush_decode),
(vorbis_dec_chain_forward):
Clear buffers used for reverse playback in _reset.
No need to set the eos flag, we clip samples using the segment.