* Add the ability to store user data in media_descriptor.
* Duration can now be retrieved from a media_instance
* Can new get the preparsed state of a media_descriptor
* Add callbacks for libvlc_MediaDescriptorDurationChanged/vlc_InputItemDurationChanged and libvlc_MediaDescriptorPreparsedChanged/vlc_InputItemPreparsedChanged.

ffmpeg demuxer (I am not sure seeking works alright). 

Use int32 rather than long for FOURCC so we don't artificially screw up the ABI on 64-bits platform. Use int64 rather than long for value so we don't overflow on 32-bits platform (ABI breakage, but I did not start it)

Revert [22699] for POTFILES.in. the make update-po rule seems to be broken on MacOSX as it's the second times that when feepk update POTFILES.in all the files in modules/ disappear

Tested with dirac files created by ffmpeg (by means of dirac support ffmpeg patch).

contrib/ffmpeg: Yet an other fix attempt for ffmpeg. (Previous fix is broken because of registers don't get reseted properly in the look).

qt4: control_(Add/Remove/Exists) are not ready yet. (and btw, the previous commit also introduced last.fm settings in the simple preferences)