[etwist] use more specific REQUEST_ENTITY_TOO_LARGE instead of BAD_REQUEST
When a request body exceeds the configured limit, return 413 to the
client instead of a generic 400.
if not rql('CWConstraintType X WHERE X name "RQLUniqueConstraint"',
ask_confirm=False):
rql('INSERT CWConstraintType X: X name "RQLUniqueConstraint"',
ask_confirm=False)