LIMIT hides duplicates. We want to know if we ever violate the
soft-constraint of path unicity in catalog, so stop setting a LIMIT.
Also, for uid lookup, LIMIT is meaningless as this is ha hard unicity
constraint (must be enforced by relational database for ERP5 to work).

Also, simplify both the DTML and the SQL by having fewer ways to be
invoked (backward-compatible).