'Constructs an order representing the reverse of the current order.
This function takes into account the effects of orders on properties not in
the group_by clause of a query. For example, consider:
SELECT A, First(B) ... GROUP BY A ORDER BY A, B
Changing the order of B would effect which value is listed in the \'First(B)\'
column which would actually change the results instead of just reversing
them.
Args:
group_by: If specified, only orders on properties in group_by will be
reversed.
Returns:
A new order representing the reverse direction.'

@datastore_rpc._positional(1)
def reversed(self, group_by=None):

    raise NotImplementedError
