Creating and displaying a plain QGLWidget on Mac would
display "garbage" or previous frame buffer content
on screen. This looks broken and raises interesting
privacy concerns.
Fix by adding a call to glClear().
Change-Id: I507c24275e41fac0be5f518c5a70d151099ae6b8 Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>