* 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.