Allow replaygain changes during playback

We have code to smoothly ramp replaygain changes,
so it's ok to update the value.  (Most likely the user
is still cueing a track so applying replaygain value
is preferred anyway)
Allow replaygain changes during playback

We have code to smoothly ramp replaygain changes,
so it's ok to update the value.  (Most likely the user
is still cueing a track so applying replaygain value
is preferred anyway)
Merge branch 'master' into allow-replaygain-while-playing
Postpone replaygain changes until track is stopped.
Merge remote-tracking branch 'origin/allow-replaygain-while-playing' into allow-replaygain-while-playing

Conflicts:
	src/basetrackplayer.cpp
Merge pull request #338 from ywwg/allow-replaygain-while-playing

Allow replaygain changes during playback