introduce globalaudiochannels and tear it down in backend dtor

vlc/backend.cpp

@@ -122,6 +122,8 @@ Backend::~Backend()
 {
     if (LibVLC::self)
         delete LibVLC::self;
+    if (GlobalAudioChannels::self)
+        delete GlobalAudioChannels::self;
     if (GlobalSubtitles::self)
         delete GlobalSubtitles::self;
 #ifdef PHONON_PULSESUPPORT

vlc/globaldescriptioncontainer.h

@@ -264,6 +264,7 @@ protected:
 template <typename D>
 GlobalDescriptionContainer<D> *GlobalDescriptionContainer<D>::self = 0;
 
+typedef GlobalDescriptionContainer<AudioChannelDescription> GlobalAudioChannels;
 typedef GlobalDescriptionContainer<SubtitleDescription> GlobalSubtitles;
 
 } // Namespace VLC