Begin experimental use of exceptions.

Provides IqTimeout and IqError which are raised when an Iq response
does not arrive in time, or it arrives with type='error'.

tests/test_stream_handlers.py

@@ -90,7 +90,10 @@ class TestHandlers(SleekTest):
             iq['id'] = 'test2'
             iq['type'] = 'set'
             iq['query'] = 'test2'
-            reply = iq.send(block=True, timeout=0)
+            try:
+                reply = iq.send(block=True, timeout=0)
+            except IqTimeout:
+                pass
 
         self.xmpp.add_event_handler('message', waiter_handler, threaded=True)