[toward py3k] rewrite has_key() (part of #2711624)
The `has_key` method is not in Python3K but dict supports __contains__ check for
ages.
ifnotrql('CWConstraintType X WHERE X name "RQLUniqueConstraint"',ask_confirm=False):rql('INSERT CWConstraintType X: X name "RQLUniqueConstraint"',ask_confirm=False)