SLING-2904 :  Simplify handling of multiple references (post processors, node name generators, post operations) 
SLING-2902 :  Post processor cache is not updated when a post processor is unbound 

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1489764 13f79535-47bb-0310-9956-ffa450edef68