title: GLKView set drawable properties
body: <p>I'm trying to port Apples GLPaint example to use GLKit. Using a UIView, its possible to return the CAEAGLLayer of the view and set the drawableProperties to include kEAGLDrawablePropertyRetainedBacking. This has the effect of retaining the drawable contents after presenting the render buffer, as expected. Removing this property results in flickering after the draw call with part of the drawable content seemingly being drawn to different buffers.</p>
  
  <p>The problem is this is exactly the issue I am now having in my GLKView, but there doesn't seem to be a way to set the drawable properties. Returning a CAEAGLLayer and setting the properties has no effect and I don't see any relevant properties of GLKView to set retained backing.</p>
  
  <p>Has anybody else come across this or have a solution?</p>