Fixes build failure on OS X, closes #44.  With the other plugins,
that's not critical, because those use the AudioOutputWrapper, which
hides this problem.

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

Make all the locks exception-safe.

Currently the switch statement is invalidated by ss.format being overwritten
with the default value of PA_SIMPLE_S16NE which results in white noise during
playback as my server is expected S16LE (S16NE).
Signed-off-by: Earnestly <zibeon@gmail.com>

This is based on a patch from Ian Scott in 2014. It was never committed,
so I figured I'd fix the outstanding issue and resubmit it.

https://www.mail-archive.com/mpd-devel%40musicpd.org/msg00139.html

The old struct config_param remains only for top-level string options.

Pulseaudio expects clients to specify their channel-map if the
default (ALSA) map does not route the audio to the expected speakers.

Many Google results suggest dealing with this by re-routing the audio
channels with the appropriate ALSA plugin, but this will then simply
break any clients which expect the default ALSA mapping.

Virtually all media files and codecs, certainly flac, dca, a52, and of
course anything based on Microsoft's WAVEFORMAT_EXTENSIBLE specification,
assume the layout in the table here:
http://en.wikipedia.org/wiki/Surround_sound#Standard_speaker_channels

Fortunately, pulseaudio directly addresses this with a built-in channel
map for WAVE-EX which can be set automatically in the stream sample-spec.

Eliminate the duplicate pa_operation_get_state() call.

There is no advantage in using g_setenv().

Passing a void pointer is unsafe.

Make it "const".

Prepare to migrate away from GLib.  Currently, we're still using GLib
as a backend.