Fix issues about namespace pg_ext_aux

[gfphoenix78]

Namespace pg_ext_aux is different from the normal namespace created by the user. It's only used internally. The user isn't allowed to create table in pg_ext_aux explicitly.

For temp table, the namespace of the auxiliary table is also pg_ext_aux, not a temp namespace. It seems complicated to distinguish pg_ext_aux and pg_ext_aux_temp. The temp table will be automatically dropped when either the table is dropped or the session is closed. The internal auxiliary relation depends on the table will also automatically dropped if its table is dropped.

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[avamingli]

LGTM.