Entity encoding was missing (for options) in generation of an xspf playlist.
On the reading side the entity decoding is all fine.
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

This reverts commit f5b8b43a.

This reverts commit 8c1d2b3e.

 - add an optional display callback,
 - make unlock callback optional (planes could be static),
 - pass an opaque picture identifier from lock to unlock and display
   callbacks (this would enable multiple pictures later),
 - pass pixel planes back to the unlock callback for convenience,
 - use pointer VLC variables instead of configuration strings,
 - fix an unlikely memory leak.

avcodec native decoder has priority over libvpx one, and I don't know
howto change that easily. Fix #3820

Fixes eg youtube viewing.

The signal handler currently does nothing anyway, so this was a waste.

Returns NULL if the variable cannot be inherited - pointers can never
be found in the configuration.

typo and double free

Also accept filter-name without +/- as enabled one, so user can see
messages by just typing module-name without any other syntax.

See http://forum.videolan.org/viewtopic.php?f=14&t=78396

So LibVLC won't try to use a video output that cannot be embedded.

We cannot drop the priority to zero. This would break rare but
functional use of `vlc --drawable-xid $WINDOWID`.

We select it explicitly when a HWND is set for embedding.

Mapping the Qt4 plugin requires a particularly long time and much
memory. So we had better avoid doing this everytime we create a new
video window (if the Qt4 interface is _not_ used).