This deadlock was a regression by commit 8e38b4f8.  Since we currently
can't resolve this, let's revert the commit, and add a GLib specific
workaround for the build failure.

This is safer, and works without epoll().  Fixes a build failure with
uClibc, which does not support epoll().

Replaces GLib's g_ascii_strcasecmp().

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

Replaces GLib's GError.

Simplify the API, don't use GLib specific integer type.

Use libasound's polling functions, implement a bridge to GSource /
GPollFD and send idle events to clients when an external program
changes the ALSA mixer volume.

Better error handling.

After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.

This allows the mixer object to access its associated audio output
object.

strcasecmp() is locale dependent, making it a bad choice for internal
string comparisons.

This allows you to select controls with duplicate names.

snd_config_update_free_global() frees cached ALSA configuration.  This
keeps valgrind a little bit more quiet.  This patch moves the call
from the open() method into the finish() method, which seems more
natural: it allows the use of the config cache, and improves the
cleanup phase.

Added an assertion in mixer_set_volume().  Removed the range checks
from the ALSA and OSS plugins.

"volume_set" is an attribute which becomes undefined when the mixer is
closed.  That means, it must be initialized each time the mixer is
opened.

The MPD core guarantees that methods are always invoked in a
consistent state.  This means we can remove lots of checks from the
volume methods.

Instead of replacing NULL with the default device in the open()
method, pass the default device to config_get_block_string().

Use config_get_block_string() instead of config_dup_block_string().

When getting or setting the volume fails, the MPD core close the
mixer.  Moved the duplicated code from the mixer plugins.

Remember if a mixer object is open or closed.  Don't call open() again
if it is already open.  This guarantees that the mixer plugin is
always called in a consistent state, and we will be able to remove
lots of checks from the implementations.

To support mixers which are automatically opened even if the audio
output is still closed (to set the volume before playback starts),
this patch also adds the "global" flag to the mixer_plugin struct.
Both ALSA and OSS set this flag, while PULSE does not.

This updates the copyright header to all be the same, which is
pretty much an update of where to mail request for a copy of the GPL
and the years of the MPD project. This also puts all committers under
'The Music Player Project' umbrella. These entries should go
individually in the AUTHORS file, for consistancy.