[FIX] purchase: analysis view must not group by quantity, otherwise identical PO...

[FIX] purchase: analysis view must not group by quantity, otherwise identical PO lines are counted only once

The product quantity is one of the columns that must be
aggregated, not used to fold PO lines into the same
result row.
This, combined with missing aggregation operators
was causing multiple identical PO lines from the
same PO to be merged together and only counted once
in some aggregations.

bzr revid: odo@openerp.com-20131105101930-f2qbcp12luom08je