ImageEngine/gaffer — pull request #770 by johnhaddon (2014-03-05 11:13:20+00:00)
Title: Fixed bug preventing positioning of nodes within Backdrops.

The collision group mechanism may seem a little more general than is needed for this particular fix, but I believe it has uses down the line, in particular for laying out individual islands of nodes separately before aligning them as required by #155.

Fixes #769.