decoder: cosmetics
decoder: merge DecoderError into DecoderProcess
decoder: Simplify DecoderWaitUnblock() proto
contrib: don't build glib by default

We only need it as a dependency of another library (fluidsynth)
playlist demux: do not use index()

marked as LEGACY in POSIX.1-2001.
POSIX.1-2008 removes the  specifications  of  index()
and rindex(), recommending strchr(3) and strrchr(3) instead.