Fix up broken query files in unit_tests/ (tested with Z3)
Setup smt2 llvm-lit tests. Z3 was used as an oracle for checking
satisfiability of queries.
Enable most .smt llvm-lit tests. Two tests have been left out

sample-smt-tests/610dd9dc.T.stp.smt_71.smt
Z3 and CVC4 spend > 5 minutes trying to solve this so I gave up
trying to write this test for now.

sample-smt-tests/zero-extend.smt
Z3 and CVC4 issue parsing errors with this test. This needs more
investigation.
Update OutputCheck submodule to new version with file extension
bug fix.
Give tests in crypto-tests proper file extension (cvc) rather than
STP.