The "sticker" command allows clients to query or manipulate the
sticker database.  This patch implements the sub-commands "get" and
"set"; more will follow soon (enumeration), as well as extended
"lsinfo" / "playlistinfo" versions.

When a song is deleted from the database, remove its sticker, too.

What's still missing is some sort of garbage collector after a fresh
database create (--create-db).

This is a wrapper for the backend sticker library.  It provides
several glue functions which take a song object instead of type/uri.

"Stickers" are pieces of information attached to existing MPD objects
(e.g. song files, directories, albums).  Clients can create arbitrary
name/value pairs.  MPD itself does not assume any special meaning in
them.

The plugin queries build-time configuration variables, and should
include config.h.

Minimize header dependencies.

Eliminate some more getBlockParam() invocations.

This replaces lots of getBlockParam() invocations.

Don't modify the configured string.

Determine the audio output name with audio_output_get_name() instead
of obtaining the name from the configuration again.

Use config_get_path() instead in mapper.c.

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

This causes a segmentation fault...

This way, we don't have to pass the full "Options" object to
daemonize().

The constructor/destructor functions parse and free the configuration
properly.  This way, we don't have to load the pid file path more than
once.

The state_file library should manage its own regular saves.

The constructor/destructor interface should hide the functions
read_state_file() and write_state_file().

config_get_path() is an simpler interface than parseConfigFilePath().

Fetch the configuration variables buffered_chunks and
buffered_before_play just when they are needed.

Moved changeToUser(), cleanUpPidFile(), killFromPidFile() to
daemon.c.  These are daemonization functions.

Without a music_directory, MPD is an excellent streaming client.

Don't include conf.h in database.c.

time(NULL) shows the wrong results when the machine's clock is
changed.

Don't use dbUtils.h functions.  This reduces 4 full database walks to
just one.

Don't recalculate the number of artists and albums each time a client
requests statistics.  Calculate that once in stats_update().

Renamed functions and types.

Don't return a writable pointer.

No "force" parameter, pass a default value instead.

Renamed functions, types, variables.

If a song is not within the music directory ("file:///..."), it has no
"parent directory".  The archive code nonetheless dereferences the
parent pointer, causing a segmentation fault.  Check parent!=NULL.

One of the previous patches made MPD consume 100% CPU in a busy wait:
when the music_pipe was full, it did not wait (with notify_wait()) for
free chunks, because a variable has a different meaning now.  Always
pass "true" as the "wait" parameter.

Some plugins used the APE or ID3 tag loader as a fallback when their
own methods of loading tags did not work.  Move this code out of all
decoder plugins, into song_file_update().

Removed yet another superfluous buffer layer: return the PCM buffer
from pcm_convert() instead of copying PCM data into the
caller-supplied buffer.