Flows no longer need to be saved between uses.

Also introduces util.positional declarations.

Reviewed in http://codereview.appspot.com/6441056/.

Fixes issue #136.
diff --git a/samples/tasks_appengine/main.py b/samples/tasks_appengine/main.py
index 54260bd..64ccb68 100644
--- a/samples/tasks_appengine/main.py
+++ b/samples/tasks_appengine/main.py
@@ -50,7 +50,10 @@
 def truncate(s, l):
   return s[:l] + '...' if len(s) > l else s
 
-application = webapp.WSGIApplication([('/', MainHandler)], debug=True)
+application = webapp.WSGIApplication([
+    ('/', MainHandler),
+    (decorator.callback_path, decorator.callback_handler()),
+    ], debug=True)
 
 
 def main():