plugins XEP-0096, XEP-0260, file: sendFile method is managed by file plugin, which choose the best available method + progress_id fix

src/plugins/plugin_xep_0166.py

@@ -275,6 +275,7 @@ class XEP_0166(object):
                 - app_args(list): args to pass to the application plugin
                 - app_kwargs(dict): keyword args to pass to the application plugin
         @param profile: %(doc_profile)s
+        @return D(unicode): jingle session id
         """
         assert contents # there must be at least one content
         client = self.host.getClient(profile)