* Added the clearBackBuffer() function to the renderbackends. * Renamed setClearScreen() to setClearBackBuffer() * The SDL render backend now honors what was set with setClearBackBuffer() * Documented testRenderedViewPort() * The OpenGL backend no longer clears the screen every frame by default. testRenderedViewPort() takes care of clearing the screen for now. Note: if the user overrides the default and enables clearing of the backbuffer that it may be cleared twice in one frame (OpenGL only)!