This reverts commit 1dfd50c2.
This is no needed of such a hack if there is no circular dependency between input and vout and if the input are properly released.

Else there is a circular dependency between the vout that yield() the input, where the vout is also an input child. This should fix properly the media_instance() tests.

stream: No use to vlc_object_yield() and object that create ourslef, and that a race could possibly corrupt in case of bad usage.

stats: Move the stat to libvlc instead of the playlist. As stated in the code it is not playlist related.

This reverts commit 69d572ca.
It's not an issue with sout-keep alone. The issue shows up if using
both sout-keep and #gather, and there is no easy way for a stream
object to know what its upstream stream (if any) is. Hence, let users
shoot themselves in the feet if they want, and otherwise assume that
people don't use #gather _in_front_ of #display.

good detection exist.