VEdit::render checking out
Cache::check_out 1
Cache::check_out 2
			VEdit::draw checking out
			Cache::check_out 1
VEdit::render checking in
						ATrack::render checking out
						Cache::check_out 1
Cache::check_in 1
			Cache::check_out 2
Cache::check_in 2
VEdit::render done
									VRender::process_buffer age video
									Cache::age_type 1
									Cache::lock_all 1
									Cache::lock_all 2
but ATrack::render has locked check_out at this point.
			VEdit::draw checking in
			Cache::check_in 1
but Cache::age_type has locked check_in and check_out can't be unlocked until
VEdit completes
