Unreasonable CPU load when using QOpenGLFramebufferObject

Run an application that renders into an FBO and thus runs QOpenGLFramebufferObject::bind() on every frame, and watch the CPU usage.

With NVIDIA drivers the CPU usage for drawing a triangle into an FBO and texturing a cube with the texture used as the color attachment for that FBO gives 19-21% CPU usage on Windows.

A big part of this is the glCheckFramebufferStatus call in bind(). Removing the call results in 0.8-1% for the same application.