[FIX] doc, new API + kanban error

- fix default_group_by in kanban
- use new api in server actions
- missing @api.multi in @compute example

Closes #6640

doc/howtos/backend.rst

@@ -764,6 +764,7 @@ method should simply set the value of the field to compute on every record in
 
         name = fields.Char(compute='_compute_name')
 
+        @api.multi
         def _compute_name(self):
             for record in self:
                 record.name = str(random.randint(1, 1e6))

doc/howtos/backend/exercise-gantt

@@ -35,7 +35,7 @@ Index: addons/openacademy/views/openacademy.xml
 ===================================================================
 --- addons.orig/openacademy/views/openacademy.xml	2014-08-28 14:21:46.543015785 +0200
 +++ addons/openacademy/views/openacademy.xml	2014-08-28 14:21:46.539015785 +0200
-@@ -145,11 +145,24 @@
+@@ -145,11 +145,23 @@
              </field>
          </record>
  
@@ -44,10 +44,9 @@ Index: addons/openacademy/views/openacademy.xml
 +            <field name="model">openacademy.session</field>
 +            <field name="arch" type="xml">
 +                <gantt string="Session Gantt" color="course_id"
-+                       date_start="start_date" date_delay="hours">
++                       date_start="start_date" date_delay="hours"
-+                    <level object="res.partner" link="instructor_id">
++                       default_group_by='instructor_id'>
-+                        <field name="name"/>
++                    <field name="name"/>
-+                    </level>
 +                </gantt>
 +            </field>
 +        </record>

doc/howtos/backend/exercise-state-workflow-actions

@@ -5,7 +5,7 @@ Index: addons/openacademy/views/session_workflow.xml
 ===================================================================
 --- addons.orig/openacademy/views/session_workflow.xml	2014-08-26 17:26:17.339783114 +0200
 +++ addons/openacademy/views/session_workflow.xml	2014-08-26 17:26:17.331783114 +0200
-@@ -6,24 +6,53 @@
+@@ -6,24 +6,50 @@
              <field name="on_create">True</field>
          </record>
  
@@ -13,8 +13,7 @@ Index: addons/openacademy/views/session_workflow.xml
 +            <field name="name">Set session to Draft</field>
 +            <field name="model_id" ref="model_openacademy_session"/>
 +            <field name="code">
-+recs = self.browse(cr, uid, context['active_ids'], context=context)
++model.search([('id', 'in', context['active_ids'])]).action_draft()
-+recs.action_draft()
 +            </field>
 +        </record>
          <record model="workflow.activity" id="draft">
@@ -32,8 +31,7 @@ Index: addons/openacademy/views/session_workflow.xml
 +            <field name="name">Set session to Confirmed</field>
 +            <field name="model_id" ref="model_openacademy_session"/>
 +            <field name="code">
-+recs = self.browse(cr, uid, context['active_ids'], context=context)
++model.search([('id', 'in', context['active_ids'])]).action_confirm()
-+recs.action_confirm()
 +            </field>
          </record>
          <record model="workflow.activity" id="confirmed">
@@ -50,8 +48,7 @@ Index: addons/openacademy/views/session_workflow.xml
 +            <field name="name">Set session to Done</field>
 +            <field name="model_id" ref="model_openacademy_session"/>
 +            <field name="code">
-+recs = self.browse(cr, uid, context['active_ids'], context=context)
++model.search([('id', 'in', context['active_ids'])]).action_done()
-+recs.action_done()
 +            </field>
          </record>
          <record model="workflow.activity" id="done">