[IMP] purchase: error message linked to product, not company
[FIX] stock: multicompany reception

When a picking is confirmed, the generated account.move(.line) should take the
company, accounts, journals and period with the same company as the picking,
not the one of the current user.

This was problematic if a user in a company confirm a picking linked to
a purchase order done in another company.
For real time valuations, the generated accounting entries were mixing both
companies.

Fixes #3466
Merge branch '7.0' of https://github.com/odoo/odoo into 7.0-linux64