Fix sync on Python 2.6.6

Python 2.6.6 has the same bug as Python 2.7, where HTTP
authentication just stops working, but does not have the
setter method to clear the retry counter. Work around by
setting the field directly if it exists.

Change-Id: I6a742e606bb7750dc66c33fc7c5d1310541db2c8
Signed-off-by: Shawn O. Pearce <sop@google.com>

main.py

@@ -287,6 +287,8 @@ class _BasicAuthHandler(urllib2.HTTPBasicAuthHandler):
       reset = getattr(self, 'reset_retry_count', None)
       if reset is not None:
         reset()
+      elif getattr(self, 'retried', None):
+        self.retried = 0
       raise
 
 def init_http():