Error evaluation tests

Added tests for error evaluation constraints, including unwind security
stuff.
Bad unwind tests and missing break/return tests

Added break/return error evaluation tests. Removed bad and impossible
unhandled unwind tests. Added note explaining why and commented out
tests
as placeholder for when we figure out how to test unhandled unwinds.
Merge pull request #4 from BrianHawley/error-assignment

Thanks for submitting the update, Brian