Blender Git Loki

Make Image and Alpha outputs in render layer node 'unavailable' when the Combined pass is not active in the render layer. Fix for bug #29999.

The internal code for render layers node is unchanged, since the buffer is created anyway. Also noticed that, while unavailable sockets and links to/from them are not displayed, they are still used in execution, which could lead to unexpected results. But that's a more general problem with the way (pseudo-)dynamic sockets are simply flagged with SOCK_UNAVAIL.