Those interfaces that need playlist deactivation can now call it
explicitly.

Media library is crap, but that is not an excuse.

That way, playlist_CurrentInput() can be called from the callbacks.

playlist_CurrentInput() could return the input that the playlist was
destroying. In principles, that was harmless, but silly.

Resetting the playing item only makes sense when there is no already
active input; NextItem() takes care of that from LoopRequest():

This code was redundant since the playlist was made tick-less (the
rebuild date check made no sense anymore).

b_active_videoplayback was not set up correctly when we wanted to prevent sleep.

(forward ported from 2.0 branch)

works with transform filter now too, fixes #7437 again.

This reverts commit 703ecf74.

This should let the kernel do the copy-on-write, only if required.
VLC does not memory copy the frames anymore.

no functional changes

(and revert earlier accidental changes)