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/oauth2client/locked_file.py b/oauth2client/locked_file.py
index 8a7aff5..8f35c90 100644
--- a/oauth2client/locked_file.py
+++ b/oauth2client/locked_file.py
@@ -23,6 +23,8 @@
 import os
 import time
 
+from oauth2client import util
+
 logger = logging.getLogger(__name__)
 
 
@@ -292,6 +294,7 @@
 class LockedFile(object):
   """Represent a file that has exclusive access."""
 
+  @util.positional(4)
   def __init__(self, filename, mode, fallback_mode, use_native_locking=True):
     """Construct a LockedFile.