Fix setting output/device for Xine and VLC backend

- Fixed setting output and device on Xine and VLC backend
- Fixed track slider for Xine, VLC and Phonon
- Improved backend settings to better support multiple backends
- Added group by samplerate and bitdepth in collection
- Fixed crash on exit when existing instance of the application is already runnung caused by NVIDIA driver
- Changed Q_OS_MAC to Q_OS_MACOS

src/collection/collection.h

@@ -73,9 +73,6 @@ class Collection : public QObject {
   void CurrentSongChanged(const Song &song);
   void Stopped();
 
- private:
-  SongList FilterCurrentWMASong(SongList songs, Song* queued);
-
  private:
   Application *app_;
   CollectionBackend *backend_;
@@ -84,10 +81,6 @@ class Collection : public QObject {
   CollectionWatcher *watcher_;
   Thread *watcher_thread_;
 
-  // Hack: Gstreamer doesn't cope well with WMA files being rewritten while being played,
-  // so we delay statistics and rating changes until the current song has finished playing.
-  QUrl current_wma_song_url_;
-
   // DB schema versions which should trigger a full collection rescan (each of those with a short reason why).
   QHash<int, QString> full_rescan_revisions_;
 };