Add basic form validation when sending new messages

This avoids the message body for now, since that's implemented a couple
different ways in the real world...

tailbone/views/messages.py

@@ -207,6 +207,7 @@ class MessagesView(MasterView):
     def make_form(self, instance, **kwargs):
         form = super(MessagesView, self).make_form(instance, **kwargs)
         if self.creating:
+            form.id = 'new-message'
             form.cancel_url = self.request.get_referrer(default=self.request.route_url('messages.inbox'))
         return form