StatisticsObjIsVisibleExt lacks "do not look in temp namespace"

StatisticsObjIsVisibleExt() lacks the "do not look in temp namespace" code of
the rest of the non-relation, non-type namespace searches. Patch attached.
See its log messages for the consequences.

Incidentally, stats on temp tables do default to a permanent schema. That
seems fine, though:

set search_path = public;
CREATE TEMP TABLE ab1 (a INTEGER, b INTEGER, c INTEGER);
CREATE STATISTICS s ON a, b FROM ab1; -- creates public.s
\dX *.*