timeline/elements: Use the _controlMask variable to match commit 5a60a7863b
viewer: Make the "TransformationBox disabled" messages FIXME instead of INFO

This prevents them from being interpreted as intentional/normal
project, timeline: Set restriction caps on tracks.
project: update tracks restriction caps when framerate is changed.
data/icons/Makefile.am: correctly name the uninstall-hook
tests: remove test_cache as it is outdated.
pipeline: When we get an error, reset _waiting_for_async_done to False.
utils/pipeline: Don't attempt recoveries more than MAX_RECOVERIES times.

MAX_RECOVERIES is set to 5 for now.
Would be good to raise a dialog when that happens in the future.
project: no need to update_restriction_caps on timeline creation.

This will be done either by adding a track or when loading the timeline.
render: set a restriction for the pixel format.
previewers: if queue is emppty, _get_wish will return True, causing
us to try to pop an empty queue.
previewers: query_success can be true and duration == -1.

In that case use track element duration.
help/Makefile.am : make distdir-help-files depend on all.
utils/pipeline: add a timeout to reset w_aiting_for_async_done.

If we didn't get ASYNC_DONE after one second.
layers: use control_container.timeline to remove the layers.
elements: Don't try to cleanup Clutter.Actors.
bin: Add support to gst-devtools
bin: Compile the 1.2 branch by default
timeline: Do not seek for operations such as sliding (moving) clips
viewer: Disable GTK double buffering to prevent flickering and black images

Fixes bug #708088 (viewer image sometimes disappears/becomes black)
Fixes bug #596954 (flickering and black image while resizing the previewer)

Also hide the internal ViewerWidget at startup until a pipeline is set,
to prevent the user's wallpaper from showing up through the viewer.