ext/flac/: Set the channel layout when decoding FLAC files with more than 2 channels...

ext/flac/: Set the channel layout when decoding FLAC files with more than 2 channels as defined by the FLAC spec. Fix...

Original commit message from CVS:
* ext/flac/Makefile.am:
* ext/flac/gstflacdec.c: (gst_flac_dec_write):
Set the channel layout when decoding FLAC files with more than 2
channels as defined by the FLAC spec. Fixes bug #534570.
Also don't try to decode left/side, right/side and mid/side files
as we don't support this at all.