removed unsafe operations in GrammarComparison
removed unsafe operations in GrammarComparison

There was a Set.clone that didn't play nicely.

joshua-decoder/thrax,jweese/thrax,jweese/thrax,joshua-decoder/thrax,joshua-decoder/thrax,tdomhan/thrax,jweese/thrax,tdomhan/thrax,dowobeha/thrax,tdomhan/thrax,joshua-decoder/thrax