temporary tablespaces in fast index creation.  The tablespaces must
reside in the same directory as the persistent tablespaces, so that
they can be renamed without copying.  Namespace collisions are avoided
by replacing the ".ibd" file name suffix with ".ib1" or ".ib2".

fil_make_ibd_name(): Treat names starting with TEMP_TABLE_PREFIX
specially.  Document the dependence on
innobase_create_temporary_tablename().