The idea behind this autotest is inspired by bug 356328 which produced
incorrect rendering results. Also it's inspired by openQA which performs
image reference comparisons.

This test case tries to go further. It creates reference images which
must match the rendering result exactly. So far the test case verifies
the start condition - kwin started and one frame is rendered with default
cursor in the middle of the screen. And it verifies the moving of the
cursor without any windows shown. Whenever the cursor moves a repaint
should be triggered and the old and new area should be properly
repainted.

To support this the test needs some minor changes in KWin:

• Scene provides a frameRendered signal - needed for waiting on frame
• Scene and SceneQPainter are exported
• SceneQPainter provides access to it's Backend, so that we get to the backbuffer
• ScriptedEffectLoader is exported for getting a list of all scripted effects - (we don't want fade to manipulate the rendering)