Make tests pass again.

Thing:
testCannotLoadClass this test collides somehow with MCGsClassModificationTestCase.
a proper fix would be

MCClassDefinition>>createClass
...
  (traitComposition ~= '{}' or: [classTraitComposition ~= '{}']) ifTrue: [
    ImproperOperation new reason: #rtErrTraitsUnsupported;
        details: 'GemStone currently does not support traits';
        object: self ; signal .
    ^ nil.
  ].
...

but then 3 out of 4 issue247 tests in MCGsClassModificationTestCase fail (or error, from time to time)