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.

The method control() is too complicated, and overengineered.  Replace
it with two trivial functions: get_volume() and set_volume().

The mixer plugins should re-use the mixer struct and incorporate it in
their object class.

Both methods are always called together.  There is no point in having
them separate.  This simplifies the code, because the old configure()
method could be called more than once, and had to free old
allocations.

Those have been superseded by the new legacy configuration code.

The plugin structures must never be modified.

Return the default value in the conf_get_block_*() functions when
param==NULL was passed.

This simplifies a lot of code, because all initialization can be done
in one code path, regardless whether configuration is present.

All config_get_block_*() functions should accept constant config_param
pointers.

This replaces lots of getBlockParam() invocations.

The g_free() function includes a NULL check.  We don't have to do it
twice.

Renamed functions, types, variables.

When MPD starts without audio output configuration, the "param"
variable is NULL.  This triggers a segmentation fault in both mixer
plugins.

removing mixer_reconfigure memmory leak, fixing configure of alsa and oss mixer (passing parameters)

This patch tryes to introduce pluggable mixer (struct mixer_plugin) along with some basic infrastructure (mixer_* functions). Instance of mixer (struct mixer) is used in
alsa and oss output plugin

There is no reason to use the shortcut "mix" instead of "mixer".