control/media_list.c: Replace set_name/name by set_media_descriptor/media_descriptor. This is the md from which the media_list is a subitem, if any.

complaints about it's inclusion in vanilla vlc on the list.

libvlc_internal.h: We have to put media_list_path here after all. We may want to privatize a bit the different libvlc types by defining, types that can be privatized, directly in the .c file. (or in a per-object .h file).

control/media_list.c: Don't send MediaListItemChanged. Listen to the MediaDescriptor* events if you need the equivalent.

control/event.c: Make detach-ing from an event safe: A detached callback can't be called after event_detached. Add an internal event_detach_lock_state, to bypass this feature.