put a gil release in the python bindings for ScriptNode::deleteNodes in case it triggers a python evaluation
Stopped ScriptNode.deleteNodes reconnecting nodes outside the script

This is so the deletion process doesn't reconnect nodes to the viewer (for example), which is a waste of effort and can cause fiddly problems like python/gil lock issues
put a GIL release in Gaffer.Plug.setInput python method
added test to make sure the script node doesn't reconnect nodes that aren't its descendants
Merge pull request #479 from davidsminor/graphpherShaderDeleteHangFix

Graphpher shader delete hang fix