Issue #1686: A test
Fix #1691
Fix a model loader hack which no longer is needed (spotted during #1691)
Issue #1691: Test for model loading sealed classes and interfaces.
Enable use of @error in the second pass of the JavacAssertionVisitor (i.e. after type checking).
(see #1691)
Test fixes related to the work on @error (see #1691). Remove @error from tests which do not have errors, or which do have errors
but whose errors are tested another way.
Make Errors.DeclarationErrorVisitor understand @error so we still generate code for things with expected errors. (see #1691).