Bunch of commits to clean up some of the SASL internals, add validation for function args, validation for data types of server responses, and some regex validation as well (e.g. base64 server responses should be valid base64). They're broken up into separate commits to make it easier to review and the final file is a bit easier to digest too.

Also removes the global asssert.throws(...) test helper as it was overwriting the real one in the built-in asserts module. The removed one did not actually check the error signature so it would report success for unrelated errors as long as the code block threw something (which was kind of confusing while testing this out...).

The only thing using that extra validation of the error signature was the SASL tests so it shouldn't break anything and all the tests pass with that change. The SASL tests have also been updated to add in some missing parameters. Previously they weren't supplying all the args needed to actually perform the tests so they'd have early or unrelated failures.