Fixes duplicate playlist entries.

False if the vector was not modified.

Send silence to all connected clients while paused, to avoid
connection interruption.

Avoid buffer underruns on the streaming client, if the encoder is "too
efficient" (e.g. when encoding silence while paused).

The ReplayGain filter clamped the gain to max. 100 % even if the
algorithm determined the signal needed a boost. That would result in any
such tracks being played with too low volume, effectively defeating the
purpose of the filter.

Unfortunately, there's no "optimized" implementation here.  We can't
use Linux's proprietary system call dup3(), because it would require
us to specify the new descriptor.

This also fixes installation when no *.gif files found in 'doc/api/html' folder.

This hack creates a copy of doc/doxygen.conf with the INPUT setting
replaced.

Free the temporary path string in apply_song_metadata().

Use the functions song_save() and song_load() to use the same format
as in the database file for those songs which need the tags.

While this is not useful for the database, it may become useful for
reusing this code for the state file.

Don't try db_get_song() if the URI has a scheme.

If a song with an absolute path points inside the music directory,
print only the relative part.  This happens when partial songs from a
playlist file were loaded.

I've already changed the "playlistinfo" command to hide HTTP
passwords, but forgot to do the same for the simpler "playlist"
command.  This patch changes queue_print_uris() to use the code from
song_print_uri().

The only caller doesn't use its return value, and the value isn't
useful anyway.

Don't use a large stack buffer.

Let the C compiler concatenate string constants.

MPD doesn't have child processes anymore, and thus we're not expecting
to receive SIGCHLD very often.  Since hard disk access isn't
interrupted by signals anyway, we don't need those excessive checks.

The function playlist_metadata_load() will overwrite the input buffer
before using the "name" parameter; since "name" points to the same
buffer, we'll get a corrupted string.

Don't open the music directory for each "lsinfo" call.  Get the list
of playlist files from the memory database.

.. and several accessor inline functions, to simplify the calling
code.