fix for digest auth when using keepalive.py
The problem was with python > 2.3 which stores part of the
headers in unredirected_hdrs.
Furthermore, we simplify the code to use httplib directly.
fix issue473
Subclass file with a __len__ method instead of setting Content-length
This is necessary for the next patch to work with python2.3
Refactor the subclassing of send()