Fix
ac218aa4f6 to work on versions before 9.5.
Unfortunately
ac218aa4f6 missed the fact that a reference to
'pg_catalog.regnamespace'::regclass wouldn't work before that type is
known. Fix that, by replacing the regtype usage with a join to
pg_type.
Reported-By: Tom Lane
Author: Andres Freund
Discussion: https://postgr.es/m/8863.
1543297423@sss.pgh.pa.us
Backpatch: 9.5-, like
ac218aa4f6