Inspired on OCA module sale_order_revision, this module was rebuilt to implement
purchase_order_revision.

On Cancelled or RFQ Sent requests for quotation/purchase orders, you can click on New Revision. This
will create a new revision of the RFQ, with the same base number and a
'-revno' suffix appended. A message is added in the chatter saying that a new
revision was created.

The old revisions of a purchase order are flagged as inactive, so they don't
clutter up searches.
