New inhibit module to prevent the power management daemon (usually gnome-power-manager) to suspend/hibernate the laptop while VLC is active.

The blend module will be loaded only if needed and reloaded on chroma change.
(As a side effect it should allow displaying TEXT even when no blending module
exist)

 As a side effect, it fixed a potential segfault (race condition) when using
sout-keep (but I am not sure if we have a stream_out module that can show the
problem)

 sout_UpdateStatistic still uses input internal data and that need to
be fixed. Audio output need such a clean too.

* fix make update-po on platforms with a non-GNU find implementation, aka BSD / Darwin. Thanks to xtophe for pointing this out and helping me

* 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).