ext/theora/theoradec.*: Port lots of changes from theoradec to theoraexpdec.

ext/theora/theoradec.*: Port lots of changes from theoradec to theoraexpdec.

Original commit message from CVS:
* ext/theora/theoradec.c: (gst_theoradec_reset),
(theora_get_query_types), (theora_dec_src_query),
(theora_dec_src_event), (theora_dec_sink_event),
(theora_handle_comment_packet), (theora_handle_type_packet),
(theora_handle_header_packet), (clip_buffer), (theora_dec_push),
(theora_handle_422_image), (theora_handle_420_image),
(theora_handle_data_packet), (theora_dec_chain),
(theora_dec_change_state):
* ext/theora/theoradec.h:
Port lots of changes from theoradec to theoraexpdec.
This catches this plugin up to theoradec. Note that duplicate frames
are broken in theoradec at the moment.