[toward-py3k] remove import with_statement (part of #2711624)
They are unneeded since we dropped python 2.5 compatibility. This will help
Python 3.3 experimentation.
if not rql('CWConstraintType X WHERE X name "RQLUniqueConstraint"',
ask_confirm=False):
rql('INSERT CWConstraintType X: X name "RQLUniqueConstraint"',
ask_confirm=False)