ext/wavpack/gstwavpackenc.*: Handle non-zero start timestamps and stream discontinuit...

ext/wavpack/gstwavpackenc.*: Handle non-zero start timestamps and stream discontinuities correctly. This only has an ...

Original commit message from CVS:
* ext/wavpack/gstwavpackenc.c: (gst_wavpack_enc_reset),
(gst_wavpack_enc_push_block), (gst_wavpack_enc_chain):
* ext/wavpack/gstwavpackenc.h:
Handle non-zero start timestamps and stream discontinuities
correctly. This only has an effect if we're muxing into
a container format as the raw WavPack stream must contain
continous sample numbers.