Print a warning when creating a cairo_t while painting

Print a warning when creating a cairo_t while painting

If you create a Cairo context in the middle of a paint run and then
you destroy it, the CairoTexture will have to upload the contents of
the image surface to the GL pipeline. This usually leads to slow
downs and general performance degradation.

ClutterCairoTexture will warn to the console if Clutter has been
compiled with the debug messages and if create() or create_region()
are called while an actor is in the middle of a paint.