The ScopeExit library uses C++11 initializers, which gcc 4.6 does not
support.  Let's kill support for this ancient incomplete C++11
compiler, nobody should be using it anymore.

Only very few (minor) features still depend on GLib.

libmp4v2 is licensed under MPL 1.1, which is incompatible with GPLv2.
Unfortunately, this means that we must remove the plugin.

More information can be found in the Debian bug report:

 http://bugs.debian.org/767504

This plugin uses the MP4v2 library to play mp4/m4a files.
It is limited to file_decode.

There hasn't been a maintainer for this plugin for years.  It may even
fail to build.

The header glib_compat.h is now obsolete and can be removed.

Look for "$XDG_CONFIG_HOME/mpd/mpd.conf", similar to where mpd looks
for the file under Windows.

This plugin has been in MPD for three years, and it has never worked.
Enough!

The hardware is obsolete, and the product does not exist anymore on
the Hauppauge web site.  Let's see if anybody complains about the
removal.

The underlying library has been obsolete for many years.

Using libopus and libogg.

Now that the libfluidsynth API was sanitized, we can enable the plugin
automatically if libfluidsynth is installed.

GLib 2.16 was released more than 4 years ago.  Let's remove some cruft
from the glib_compat.h header, and avoid new cruft to it.

libOggFLAC has been deprecated for 5 years now, and we havn't been
testing it for a long time.  Let's delete it.

Using libffado, to play on firewire audio devices.

Warning: this plugin was not tested successfully.  I just couldn't
keep libffado2 from crashing.  Use at your own risk.

For details, see my Debian bug reports:

  http://bugs.debian.org/601657
  http://bugs.debian.org/601659

Drop the required GLib version from 2.16 to 2.12, because many current
systems still don't have GLib 2.16.  This requires several new
compatibility functions in glib_compat.h.

Accidently, MPD has been using several GLib 2.16 functions for a
while, and nobody noticed yet.  To simplify the code base, let's bump
the minimum GLib version for MPD to 2.16.  That version is old enough,
and it's reasonable to expect users to have it.

Still missing:
- seeking
- tags
- streaming
- encodings other than MPG123_ENC_SIGNED_16