gst/wavenc/: Add support for a-law and mu-law encoded wav files. Fixes bug #562434.

gst/wavenc/: Add support for a-law and mu-law encoded wav files. Fixes bug #562434.

Original commit message from CVS:
Patch by: Pepijn Van Eeckhoudt
<pepijn dot vaneeckhoudt at luciad dot com>
* gst/wavenc/gstwavenc.c: (gst_wavenc_create_header_buf),
(gst_wavenc_sink_setcaps), (gst_wavenc_change_state):
* gst/wavenc/gstwavenc.h:
* gst/wavenc/riff.h:
Add support for a-law and mu-law encoded wav files. Fixes bug #562434.