T-entailment work, and QCF (quant conflict find) work that uses it.

This commit includes work from the past month on the T-entailment check
infrastructure (due to Tim), an entailment check for arithmetic
(also Tim), and QCF work that uses T-entailment (due to Andrew Reynolds).

Signed-off-by: Morgan Deters <mdeters@cs.nyu.edu>
decision engine: cache start index for and/or nodes

This is done only in "hard" case. Limited testing has not shown
improvement in the "easy" case.

This was triggerred by a benchmark sent by andy/viktor.

performance comparison notes for the change on wiki
http://church.cims.nyu.edu/wiki/User:Kshitij/decisioncacheindex
Merge remote-tracking branch 'upstream/master' into sets
Minor optimizations to datatypes, revert to checkClash not mod eq.  Minor clean up.