Fix Contraction

{A(X), A(b) |- B(X)} now contracts correctly
Add Contraction test case
Fix Contraction 

Now does multiple contractions at once
Remove ProcessResolution from FOLowerUnits
Change FOLowerUnits

UnifyingResolutionMRR calls were changed to UnifyingResolution, with 
the additional contractions done later.
Fix FOLowerUnits

Changed UnifyingResolution call back to UnifyingResolutionMRR; without
it, the third test case fails. Kept additional contraction checks at
the end.
Fix FOLowerUnits

Addresses first comment of
https://groups.google.com/d/msg/skeptik-dev/E3xw84nThCw/0Izqdf_nQMkJ