VLCMediaThumbnailer: use a private VLCLibrary instance with single threaded avcodec decoding
VLCMediaThumbnailer: use a private VLCLibrary instance with single threaded avcodec decoding

kamcord/VLCKit,CollabraMusic/VLCKit,larrytin/VLCKit,programming086/VLCKit,waterskier2007/VLCKit,siuying/VLCKit,strukturag/VLCKit,programming086/VLCKit,i386/vlckit,simon1984/test,kamcord/VLCKit,waterskier2007/VLCKit,simon1984/test,larrytin/VLCKit,CollabraMusic/VLCKit,siuying/VLCKit,CollabraMusic/VLCKit,siuying/VLCKit,simon1984/test,strukturag/VLCKit,waterskier2007/VLCKit,hpsoar/VLCKit,brion/VLCKit,kamcord/VLCKit,hpsoar/VLCKit