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

extras/contrib/src/Makefile: Fix dca an zvbi install name (on Mac OS X in particular). (Reported by maru).

We now have:
 1x 1.5x 2x 3x 4x 8x (and the same for slower).

MacOSX/Framework/VLCLibrary.m: Regroup the sharedLibrary allocation and release. Fix a warning due to a left over in previous commit.

MacOSX/Framework/VLCLibrary.m: Better memory management for the global VLCLibrary object. Give an autoreleased object in +[VLCLibrary sharedLibrary]. Release the global VLCLibrary atexit.

Destroying the instance object while a descriptor is still alive will crash(!).
I wonder why libvlc_instance_t is not reference counted as the other handler types... ?

Changing the order of parameters may be needed, but changing the parameters themselves is definitely not (it would crash in some cases anyway): add some const qualifiers