screensaver: removes unused variable

Better solution would be to make sure interface threads lock their object ALL THE TIME, except when waiting on its condition variable, so we do never "loose" condition signals. However, I am not sure if this would not result in a deadlock, should the interface need to lock another object (typically, playlist, input and/or vout).  Also, we would need to have all thread call vlc_thread_ready(), otherwise, we could also miss the signal if it happens right after the thread is created => this requires fixing every interface, except those that don't have a pf_run.

dbus: monitors input "state" variable to emit the TrackChange signal only when the metadata has been read

- Enable building of libamrnb and libamrwb (disabled by default). To enable add HAVE_AMR to config.mak and make sure to rebuild ffmpeg too.
- Bumped up libdvbpsi version number to 0.1.6

configuration: add config_AddIntf() config_RemoveIntf() and config_ExistIntf() to handle extra interfaces in the preferences
make use of it for last.fm simple preferences (ref #1262)
by the way the duplication of "control" with "extraintf" is very boring

qt4: delete the QApplication when we are finished using it, removes an ugly QObject::killTimers warning.

playlist_Clear() should delete only the local playlist, not the root playlist (including the media library, and the read only services discovery)

remove warning about libvlc and libvlc-control not being valid plugins