Use underscore method name.

Since camelcase names are aliased to the underscored name at startup,
if the underscored version is replaced later, the camelCase name does
not reflect the change.

sleekxmpp/stanza/iq.py

@@ -77,7 +77,7 @@ class Iq(RootStanza):
         StanzaBase.__init__(self, *args, **kwargs)
         if self['id'] == '':
             if self.stream is not None:
-                self['id'] = self.stream.getNewId()
+                self['id'] = self.stream.new_id()
             else:
                 self['id'] = '0'