[IMP] ir.actions: add Warning in eval context for server actions

This way one can do `raise Warning(Foo)` to abort
a transaction and show a user-friendly warning to
the user.

bzr revid: odo@openerp.com-20140403162650-m7zmmr9dba7jnzxp

openerp/addons/base/ir/ir_actions.py

@@ -935,6 +935,7 @@ class ir_actions_server(osv.osv):
             'uid': uid,
             'user': user,
             'context': context,
+            'Warning': openerp.exceptions.Warning,
         }
         return eval_context