plugins: added new MissingModule exceptions to plugins using third party modules

src/plugins/plugin_xep_0277.py

@@ -31,7 +31,10 @@ from sat.tools import sat_defer
 
 # XXX: tmp.pubsub is actually use instead of wokkel version
 from wokkel import pubsub
-from feed.date import rfc3339
+try:
+    from feed.date import rfc3339
+except ImportError:
+    raise exceptions.MissingModule(u"Missing module pyfeed, please download/install it from http://home.avvanta.com/~steveha/pyfeed.html")
 import uuid
 import time
 import urlparse