Mostly resolves bug #561 memory leaks, and more.
Fix for (user) context-dependence of arith TO_INT/IS_INT rewriting and rewrite-divk.
Fix simplify output for SMT2 printer.
Fix compiler warning re: TheoryUF destructor.
Fix warnings, cleanup in strings typechecker.
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>