Assertion failure from plan cache invalidation

This leads to assertion failure, on versions 8.3 onwards where plan
cache invalidation was introduced:

postgres=# CREATE FUNCTION ttfunc() RETURNS VOID AS $$
begin
   PERFORM * FROM temptable;
END;
$$ LANGUAGE plpgsql;
CREATE FUNCTION
postgres=# begin;
BEGIN
postgres=# CREATE TEMPORARY TABLE temptable (id int4);
CREATE TABLE
postgres=# SELECT ttfunc();
  ttfunc
--------

(1 row)

postgres=# rollback;
ROLLBACK
postgres=# SELECT ttfunc();
server closed the connection unexpectedly
    This probably means the server terminated abnormally
    before or while processing the request.

TRAP: FailedAssertion("!(((bool) ((myTempNamespace) != ((Oid) 0))))",
File: "namespace.c", Line: 2705)

PushOverrideSearchPath() assumes that if the temporary namespace existed
when an override search path was memorized with GetOverrideSearchPath(),
it must still exist. That's not true in the above example, rolling back
the transaction that the temporary namespace was created in drops it.

--
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com