Allow extracting machine-readable object identity

Introduce pg_identify_object(oid,oid,int4), which is similar in spirit
to pg_describe_object but instead produces a row of machine-readable
information to uniquely identify the given object, without resorting to
OIDs or other internal representation.  This is intended to be used in
the event trigger implementation, to report objects being operated on;
but it has usefulness of its own.

Catalog version bumped because of the new function.
Fix "element <@ range" cost estimation.

The statistics-based cost estimation patch for range types broke that, by
incorrectly assuming that the left operand of all range oeprators is a
range. That lead to a "type x is not a range type" error. Because it took so
long for anyone to notice, add a regression test for that case.

We still don't do proper statistics-based cost estimation for that, so you
just get a default constant estimate. We should look into implementing that,
but this patch at least fixes the regression.

Spotted by Tom Lane, when testing query from Josh Berkus.