TODO

>
> * Allow a database in tablespace t1 with tables created in tablespace t2
>   to be used as a template for a new database created with default
>   tablespace t2
>
>   All objects in the default database tablespace must have default tablespace
>   specifications.  This is because new databases are created by copying
>   directories.  If you mix default tablespace tables and tablespace-specified
>   tables in the same directory, creating a new database from such a mixed
>   directory would create a new database with tables that had incorrect
>   explicit tablespaces.  To fix this would require modifying pg_class in the
>   newly copied database, which we don't currently do.