[IMP] Document the description fields on Products, and assume that invoices must get either the Purchase Description or the Sale Description.
[FIX] borrow an additionnal fix from lp:~openerp-dev/openobject-addons/trunk-bug-1101146-rmu
[FIX] purchase/sale description helps are inverted - borrowed from lp:~openerp-dev/openobject-addons/trunk-bug-1101146-rmu
[MERGE] [FIX] account: use the purchase or sale description for manual invoicing instead of product description, courtesy of Numérigraphe