Renamed functions and variables.

Moved code which deals with all audio outputs at once into a separate
library.

This function isn't used anymore.

The crossfading code shouldn't depend on the audio output code.  Pass
the current audio format to cross_fade_calc() and let it compare
directly, instead of using isCurrentAudioFormat().

When MPD is stopped, but the last song is still the "current song",
and you delete it, playlist->current is not updated, and becomes an
invalid value.  Fix this by catching "!playlist->playing &&
playlist->current == (int)songOrder".

Added audio_output_get(), audio_output_find().

audio_output_config_count() returns the number of audio outputs in the
configuration file.  It is only used by initAudioDriver().  The public
function audio_output_count() now returns audioOutputArraySize.

output_api.h is required for enum audio_output_command.

Assertions on pc.command and pc.next_song.

When we reset pc.next_song if there is no song queued, this might
cause a race condition: the next song to be played is cleared, while
pc.command was already set.  Clear the "next_song" only if there is a
song queued for the current do_play() invocation.

If a new song is queued before calling playerSeek(), then the player
and the playlist enter an inconsistent state, because the player
discards the playlist's "queued" song in favor of the seeked song.

Call playlist_update_queued_song() after playerSeek().

After a player command (successful or not), reset pc.next_song,
because the queue is supposed to be empty then.  Otherwise,
playlist.queued and pc.next_song may disagree, which triggers an
assertion failure.

Commit f78cddb4 introduced a regression: after a song was moved, the
order array was not updated (in random mode).  This caused MPD to
think the "current" song has changed when you moved something to the
position of the current song.

Don't define HAVE_FFMPEG if the ffmpeg libraries were found via
pkg-config, but ffmpeg support was disabled because
avcodec_decode_audio2() is not available.

Check if the "current+1" position is actually valid.

Including "../config.h" breaks on some systems.

Always assume the buffer is empty before calling the encoder.  Always
flush the buffer immediately after there has been added something.
This reduces the risk of buffer overruns, because there will never be
a "rest" in the current buffer.

Don't duplicate the tag received by the send_metadata() method - send
it to the shout server directly.

Removed the manual timer synchronization from the shout plugin.
libshout's shout_sync() function does it for us.

The non-blocking mode of libshout is sparsely documented, and MPD's
implementation had several bugs.  Also removed connect throttling
code, that is done by the MPD core since 0.14.

When shout_data.tag!=NULL, there is a "tag to send".  The tag_to_send
flag is redundant.

That variable is set in handle_shout_error(), but is never read.

In random mode, this patch allows clients to see the "next song" in
the queue.

After the state file has been loaded, the playlist version is still
"1", and "plchanges 1" returns the whole playlist.  Fix this by
increasing the playlist version after the state file has been loaded.

If stickers are not configured at runtime, don't call
sticker_song_delete().

spl_save_playlist() is a wrapper for spl_save_queue().

Removed the explicit "playlist:" prefix from all log messages.

Hide the details of the playlist behind wrapper functions.

Pass constant playlist objects to functions which do not modify it.

Return true on success, instead of 0.  Converted the "detail"
parameter to bool.

Renamed one function.

Moved functions for playlist editing (append, delete, shuffle, move)
to playlist_edit.c.

Moved handlers for control commands (play, stop, next, prev) to
playlist_control.c.

Don't call syncPlaylistWithQueue() in nextSongInPlaylist() and
previousSongInPlaylist().  This is a relic from the time when there
was no event, and was a workaround to the timing problem.

Export the "g_playlist" variable, and pass it to all playlist
functions.  This way, we can split playlist.c easier into separate
parts.  The code which initializes the singleton variable is moved to
playlist_global.c.

Moved everything related to saving or loading the playlist from/to the
state file to playlist_state.c.