* clutter/clutter-feature.h:
Add new stage feature flags and document.
* clutter/eglnative/clutter-backend-egl.c:
* clutter/eglx/clutter-backend-egl.c:
* clutter/sdl/clutter-backend-sdl.c:
Set new feature flags.
* clutter/glx/clutter-backend-glx.c:
* clutter/glx/clutter-stage-glx.c:
* clutter/clutter-stage.c:
* clutter/clutter-stage.h:
Add a 'user_resizeable' setting to the backend and implement
for glx backend.
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