[FIX] point_of_sale: better default sale journal for new pos.config, use company of current user

done to fix test in 01_order_to_payment.yml when creating pos.order
default config can have journal of different company, will get exception if done with a journal of main company

bzr revid: mat@openerp.com-20130814134511-c0f3z27f9p2gflt6