[FIX] project: project preference field must be editable

The user preferences screen is kind of a hack
because it lets the user modify fields on a
model that is normally read-only for her (res.users).
This is accomplished by a custom write() method
on res.users combined with a view on which some
fields are forced to be read-write using a
trick: @readonly=0.

bzr revid: odo@openerp.com-20120312102001-aas39wknhsyxkhbx

addons/project/project_view.xml

@@ -676,7 +676,7 @@
          <field eval="18" name="priority"/>
          <field name="arch" type="xml">
             <group name="default_filters" position="inside">
-                <field name="context_project_id" context="{'user_preference':True}" widget="selection"/>
+                <field name="context_project_id" context="{'user_preference':True}" widget="selection" readonly="0"/>
             </group>
        </field>
     </record>