gst/matroska/matroska-demux.c: Fix EBML-laced block parsing. Diffs are relative to previous lace, not the first lace....

Original commit message from CVS:
2004-01-04  Ronald Bultje  <rbultje@ronald.bitfreak.net>

* gst/matroska/matroska-demux.c:
Fix EBML-laced block parsing. Diffs are relative to previous
lace, not the first lace. Thanks to Mosu from the Matroska
team for detecting this.
(gst_matroska_demux_parse_blockgroup):
* gst/wavparse/gstwavparse.c: (gst_wavparse_init),
(gst_wavparse_parse_fmt), (gst_wavparse_getcaps),
(gst_wavparse_handle_sink_event), (gst_wavparse_loop),
(gst_wavparse_change_state):
* gst/wavparse/gstwavparse.h:
Quickfix for capsnego.