. Added a missing mutex_unlock in video_output.c

 . Added a missing mutex_unlock in video_output.c
 . Moved a mutex_destroy after the thread cancellation to prevent
   possible problems
 . Added a missing #ifdef in intf_msg.c which prevented compilation
   with --enable-debug
 . Fixed a bug in the input that prevented to quit properly in certain
   cases (some ES were not deleted because their index was skipped when
   the former one was deleted, well Meuuh should know what I mean)

  There is still a segfault when quitting, most presumably in the
 audio output. I couldn't find what causes it yet.