[storm] group_by with order_by

[Gustavo Niemeyer]

Hey Akira,

> has anyone tried using "group_by" and "order_by" in the same query
> together group_by alone works, but when one adds order-by to the query
> one gets errors.

The compilation of these expressions was tested, but since we
don't have support for group_by in the Store yet, we overlooked
the ordering, and had no tests ensuring that it worked on backends.

I've just committed a fix to trunk, and included a test to make sure
that the expression continues to work in all backends in the future.

Thank you very much for reporting it.

-- 
Gustavo Niemeyer
http://niemeyer.net