Rearrange order of operations in heap_create_with_catalog so that if

two transactions create the same table name concurrently, the one that
fails will complain about unique index pg_class_relname_index, rather than
about pg_type_typname_index which'll confuse most people.  Free side
benefit: pg_class.reltype is correctly linked to the pg_type entry now.
It's been zero in all but the preloaded pg_class entries since who knows
when.