replay_gain: added setting "replaygain off"

doc/mpd.conf.5

@@ -168,7 +168,7 @@ only choice) if MPD was compiled without libsamplerate.
 For an up-to-date list of available converters, please see the libsamplerate
 documentation (available online at <\fBhttp://www.mega-nerd.com/SRC/\fP>).
 .TP
-.B replaygain <album or track>
+.B replaygain <off or album or track>
 If specified, mpd will adjust the volume of songs played using ReplayGain tags
 (see <\fBhttp://www.replaygain.org/\fP>).  Setting this to "album" will adjust
 volume using the album's ReplayGain tags, while setting it to "track" will

doc/mpdconf.example

@@ -299,8 +299,8 @@ input {
 # Normalization automatic volume adjustments ##################################
 #
 # This setting specifies the type of ReplayGain to use. This setting can have
-# the argument "album" or "track". See <http://www.replaygain.org> for more
-# details. This setting is disabled by default.
+# the argument "off", "album" or "track". See <http://www.replaygain.org>
+# for more details. This setting is off by default.
 #
 #replaygain			"album"
 #

src/replay_gain.c

@@ -44,7 +44,7 @@ void replay_gain_global_init(void)
 {
 	const struct config_param *param = config_get_param(CONF_REPLAYGAIN);
 
-	if (param == NULL) {
+	if (param == NULL || strcmp(param->value, "off") == 0) {
 		replay_gain_mode = REPLAY_GAIN_OFF;
 	} else if (strcmp(param->value, "track") == 0) {
 		replay_gain_mode = REPLAY_GAIN_TRACK;