Rename tests

Two rename tests - one which *passes* on the updates (yay!), included for regression testing and one which still fails.

The failing unit test is a case where two renames exist:  A->B and B->C.  We correctly map the A->B rename and merge the A source data into the B target.  When we next examine the C target, we look at B as a source, but B has been rewritten with the new source data from the previous step and we reject it as a rename source candidate.