Support additional args/kwargs on cursor method

fdbsql has an optional nested kwarg, which is supported in the
actual code, but not in the testing proxy
Print useful traceback on error

_expect_failure was rethrowing the exception without keeping the
traceback, so it was really hard to find out what was actually wrong
Added new requirement for check_constraints
Forgot to update usage of ex to exc_value
Added requirement to test for bind limit
require check constraints for tests
Set the length for MyType implementation

Mysql drops the type in these tests, when it does visit_typeclause,
 since it's an unkown type it just says none,
and doesn't do a cast.
Firebird also doesn't support varchar with length, it throws an
error on these types.
Added requirement for temporary tables
Removed accidental print statements
Merge branch 'master' into fdbsql-tests

Conflicts:
	lib/sqlalchemy/testing/exclusions.py
It now calls raise_from_cause

master was updated to call util.raise_from_cause which is better
than what I had
Merge remote-tracking branch 'origin/pr/151' into pr151