[FIX] purchase: canceled PO can not be selected to create a bill

[IMP] purchase: name_get, show the amount (to select a PO in the bill
when several PO for the same vendor)

addons/purchase/invoice_view.xml

@@ -58,7 +58,7 @@
         <field name="inherit_id" ref="account.invoice_supplier_form"/>
         <field name="arch" type="xml">
             <field name="reference" position="after" >
-                 <field name="purchase_id" attrs="{'invisible': [('state', '&lt;&gt;', 'draft')]}" class="oe_edit_only" 
+                 <field name="purchase_id" attrs="{'invisible': [('state', '=', 'purchase')]}" class="oe_edit_only" 
                     options="{'no_create': True}"/>
             </field>
             <xpath expr="//field[@name='invoice_line_ids']/tree/field[@name='company_id']" position="after">

addons/purchase/purchase.py

@@ -9,6 +9,7 @@ from openerp.tools.translate import _
 from openerp.tools.float_utils import float_is_zero, float_compare
 import openerp.addons.decimal_precision as dp
 from openerp.exceptions import UserError, AccessError
+from openerp.tools.misc import formatLang
 from openerp.addons.base.res.res_partner import WARNING_MESSAGE, WARNING_HELP
 
 class PurchaseOrder(models.Model):
@@ -178,6 +179,8 @@ class PurchaseOrder(models.Model):
             name = po.name
             if po.partner_ref:
                 name += ' ('+po.partner_ref+')'
+            if po.amount_total:
+                name += ': ' + formatLang(self.env, po.amount_total, currency_obj=po.currency_id)
             result.append((po.id, name))
         return result