lp:~numerigraphe-team/openobject-addons/7.0-delivery-button-states-on-po

On the purchase order form there is a button "Incoming Shipments" which is visible only for POs in the state "approved".
This is not enough: users need this button in other states to, for example to examine the delivery situation when the state is "delivery exception".
This branch make the button behave like the button "Invoices": visible in all states but draft, which makes more sense.

Fixes https://github.com/odoo/odoo/issues/256

Superseded by https://github.com/OCA/OCB/pull/25