Blender Git Loki

A slightly different way of dealing with the shift problem that doesn't involve a hack. It also changes the design of the layer buttons slightly such that clicking one doesn't automatically reset the others, which I think may be a usability improvement anyway as their purpose is to act like layers, which should be independent of each other. To make up for this I've added a ctrl-click which acts as before, selecting a single layer to the exclusion of others.