Port mplex element to 0.10. Fixes bug #520329.

Port mplex element to 0.10. Fixes bug #520329.

Original commit message from CVS:
Patch by: Mark Nauwelaerts <manauw at skynet dot be>
* configure.ac:
* ext/Makefile.am:
* ext/mplex/Makefile.am:
* ext/mplex/gstmplex.cc:
* ext/mplex/gstmplex.hh:
* ext/mplex/gstmplexibitstream.cc:
* ext/mplex/gstmplexibitstream.hh:
* ext/mplex/gstmplexjob.cc:
* ext/mplex/gstmplexjob.hh:
* ext/mplex/gstmplexoutputstream.cc:
* ext/mplex/gstmplexoutputstream.hh:
Port mplex element to 0.10. Fixes bug #520329.
* tests/check/Makefile.am:
* tests/check/elements/mplex.c: (test_sink_event), (setup_src_pad),
(teardown_src_pad), (setup_mplex), (cleanup_mplex),
(GST_START_TEST), (mplex_suite), (main):
Add unit test for the mplex element.