[FIX] stock: before creating chained pickings, regroup moves by chained auto packing

[FIX] stock: before creating chained pickings, regroup moves by chained auto packing

Before, all moves issued from a same purchase order were put in the same chained picking, and, therefore, the moves were all treated with the same behavior (manually, automaticaly, ...)

bzr revid: dle@openerp.com-20140415160331-kzgib87qabvpc86p