One fix for bug [#33785] compositor is (unnecessarily?) slow
Added additional buffers - new subtree - for groupnodes.
One needs to be aware of how groupnodes should be created. 
Having translate & scale nodes, with the translate inside the groupnode and the scale node outside, causes artefacts.
Both should be inside or outside the groupnode. Same holds for other distort nodes. 
  


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54281 954f8c5b-7b00-dc11-b283-0030488c597c