gst/mpegaudioparse/gstmpegaudioparse.*: Make timestamp handling in mp3parse saner...

gst/mpegaudioparse/gstmpegaudioparse.*: Make timestamp handling in mp3parse saner; now works for at least simple cases.

Original commit message from CVS:
* gst/mpegaudioparse/gstmpegaudioparse.c:
(mp3_type_frame_length_from_header), (gst_mp3parse_reset),
(gst_mp3parse_init), (gst_mp3parse_dispose),
(gst_mp3parse_sink_event), (gst_mp3parse_chain), (head_check),
(gst_mp3parse_change_state):
* gst/mpegaudioparse/gstmpegaudioparse.h:
Make timestamp handling in mp3parse saner; now works for at least
simple cases.