Fix #34948, bug in Cycles node groups. The proxy node maps used to identify external connections of node group nodes were having name clashes with input/output sockets of the same name, leading to invalid cyclic connections in the cycles shader graph that were subsequently removed (prints warnings in terminal). Solution is to use two separate maps for inputs and outputs so group node sockets can safely use the same identifier.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55955 954f8c5b-7b00-dc11-b283-0030488c597c