Naive but effective fix for JENA-494 which should work for most cases.

Essentially compares the visible variables in the original algebra vs the rename reversed algebra to determine if a remapping of variable names is necessary.  When it is it wraps the query iterator returned with a special variable remapping query iterator.

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1563376 13f79535-47bb-0310-9956-ffa450edef68