Fix group by access error on stock.picking.in/out in multi company by ensuring...

Fix group by access error on stock.picking.in/out in multi company by ensuring the good ir rules are applied, this is done by calling read_group using stock.picking intead of stock.picking.in/out.

lp bug: https://launchpad.net/bugs/1309105 fixed

bzr revid: yannick.vaucher@camptocamp.com-20140417164953-7bjuggmhktv7mfwx