Usability fix, own collection.

If you have two windows, each with different scene, the render output for a window
would go to the other, if it was already drawing a render for the other scene.

Now you can have renders draw correct in two windows for two scenes.



git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56011 954f8c5b-7b00-dc11-b283-0030488c597c