ext/theora/: Mark discontinuities of > 3/4 of a frame, reinit encoder.

ext/theora/: Mark discontinuities of > 3/4 of a frame, reinit encoder.

Original commit message from CVS:
* ext/theora/gsttheoraenc.h:
* ext/theora/theoraenc.c: (gst_theora_enc_init),
(theora_enc_reset), (theora_enc_clear), (theora_enc_sink_setcaps),
(theora_buffer_from_packet), (theora_enc_is_discontinuous),
(theora_enc_chain), (theora_enc_change_state):
Mark discontinuities of > 3/4 of a frame, reinit encoder.

* tests/check/pipelines/theoraenc.c: (check_buffer_granulepos),
(GST_START_TEST), (theoraenc_suite):
Enable discontinuity test, fix it.