[IMP] purchase: usability improvements

- Task: https://www.odoo.com/web#id=5342&view_type=form&model=project.task&action=333&active_id=131
yes you are right, but as per the task point  (when user enter 005 or sustek or product description, it seacrh on it ) means if user enter sustek instead of Asustek we have to search on it so thats why i have done this changes.