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

A song index cannot be negative.  Also require the second parameter to
be valid.

In a range "start:end", "end" itself should not be included.  Use the
same semantics as other languages implementing ranges, e.g. Python.

Loosely based on a patch provided by lesion in bug #1766. The playlistinfo
command can now retrieve ranges of the playlist. The new argument indicates
which entry is the last one that will be displayed. The number of displayed
entries may be smaller than expected if the end of the playlist is reached.

Previous usage:
playlistinfo [start]

New usage:
playlistinfo [start[:end]]

A range argument looks like start[:end] and is used to specify the entries
of a list that should be returned (rather than the whole list).

Don't use fixed static buffers.  GLib allocates a new string for us
anyway, let's just return this one instead of copying it.

The archive code was disabled, because config.h was not included and
thus ENABLE_ARCHIVE was not defined.

Save an empty database, even if the music directory is empty.

Use the PCM buffer library for the libsamplerate output buffer.

Return a temporary buffer from pcm_resample_*() and pcm_convert().

Replace a "static" buffer with the PCM buffer library.

Replace a "static" buffer with the PCM buffer library.

This library allocates temporary buffers for storing PCM conversion
results.  It should replace all those "static" buffer variables which
are racy and never freed.

Be sure that the output thread has quite before we start destructing
the output object.

Free memory allocated by the notify object (GMutex, GCond) when it's
not used by the output object anymore.

Free memory allocated by libsamplerate when the output or the decoder
is closed.

1024 is 2^10, and allows gcc to use bit shift operations instead of
multiplication / division.

In generic PCM functions allowing all sample formats, pass a void
pointer instead of a char pointer.

All what's left in pcm_utils.h is the pcm_range() utility function,
which is only used internally by pcm_volume and pcm_mix.

The function does not need the full pcm_convert_state struct.

Moved all code which converts the sample format to a separate library.

Moved the software mixing code (used by crossfading) to a separate
library.

Moved the software volume code to a separate library.

We are going to split the pcm_utils.c library, and pcm_range() will be
useful for several sub libraries.

Get rid of the non-portable Linux list library, part III (final).

Get rid of the non-portable Linux list library, part II.

Get rid of the non-portable Linux list library, part I.

Fix a typo in the icy-metadata patch.

Declare and initialize MPD_LIBS and MPD_CFLAGS before the "OS specific
defaults" section.

Both are unused.