Added ability to move to previous item in the media list player playlist. Added playback modes to allow for automatic looping and repeating of playlist items. Fixed a race condition with Pause and Play functions by adding appropriate locks to these functions. Added automated testing for previous item and playback options.
Signed-off-by: Pierre d'Herbemont <pdherbemont@free.fr>

Partially revert 30f9eb49

* remove unneded p_sys variables (p_xml)
* fix memleaks.
* fix object leaks.

seems that noone is using it actually).

Only blu-ray subtitle are enabled.
If other formats are to be enabled, they must be carefully tested.

It will be used for blu-ray subtitles.

This solves the Sony Wave float32 sample on little endian machines.
Of course the float64 sample doesn't work yet, because of the lack of converter.

(or maybe it was Aesthetics)