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/threadqueue/main.py b/samples/threadqueue/main.py
index 817de59..5b9764a 100644
--- a/samples/threadqueue/main.py
+++ b/samples/threadqueue/main.py
@@ -100,7 +100,7 @@
       backoff = Backoff()
       while backoff.loop():
         try:
-          response = request.execute(http)
+          response = request.execute(http=http)
           print "Processed: %s in thread %d" % (response['id'], n)
           break
         except HttpError, e: