Allow to reset to draft a cancelled sale

review360001

sale.py

@@ -181,13 +181,16 @@ class Sale(Workflow, ModelSQL, ModelView):
                 ('draft', 'cancel'),
                 ('quotation', 'cancel'),
                 ('quotation', 'draft'),
+                ('cancel', 'draft'),
                 ))
         self._buttons.update({
                 'cancel': {
                     'invisible': ~Eval('state').in_(['draft', 'quotation']),
                     },
                 'draft': {
-                    'invisible': Eval('state') != 'quotation',
+                    'invisible': ~Eval('state').in_(['cancel', 'quotation']),
+                    'icon': If(Eval('state') == 'cancel', 'tryton-clear',
+                        'tryton-go-previous'),
                     },
                 'quote': {
                     'invisible': Eval('state') != 'draft',

sale.xml

@@ -91,8 +91,7 @@ this repository contains the full copyright notices and license terms. -->
                                 <group col="7" colspan="2" id="buttons">
                                     <button name="cancel" type="object" string="Cancel"
                                         icon="tryton-cancel"/>
-                                    <button name="draft" type="object" string="Draft"
-                                        icon="tryton-go-previous"/>
+                                    <button name="draft" type="object" string="Draft"/>
                                     <button name="quote" type="object" string="Quote"
                                         icon="tryton-go-next"/>
                                     <button name="%(wizard_invoice_handle_exception)d"