[req.find] Use vreg.schema.eschema for eschema lookup If an etype is non-existant, using vreg.schema[etype] raises a confusing error complaining about a non-existing relation. This is because of the implementation of vreg.schema.__getitem__ that look first in entities and then in relations. Using directly vreg.schema.eschema restrict the lookup to etypes only, hence raises a meaningful error when the etype does not exist.

if not rql('CWConstraintType X WHERE X name "RQLUniqueConstraint"',
           ask_confirm=False):
    rql('INSERT CWConstraintType X: X name "RQLUniqueConstraint"',
        ask_confirm=False)