examples/attach: more robust check for a successful bind

<bind> is not necessarily the first child element of <success> (it isn't
in the XML returned from Prosody 0.8).  Therefore, to robustly check if
a bind succeeded, we must check *all* the children of <success> for a
<bind> element.

examples/attach/boshclient.py

@@ -110,7 +110,13 @@ def startSessionAndAuth(self, hold='1', wait='70'):
                     if elems[0].name == 'success':
                         retb, elems = self.sendBody(self.buildBody())
 
-                        if elems[0].firstChildElement().name == 'bind':
+                        has_bind = False
+                        for child in elems[0].children:
+                            if child.name == 'bind':
+                                has_bind = True
+                                break
+
+                        if has_bind:
                             iq = domish.Element(('jabber:client', 'iq'))
                             iq['type'] = 'set'
                             iq.addUniqueId()