The old use of Eventlet's posthook process meant that responses that
forgot to include content-length or transfer-encoding headers would
get one tacked on, if Eventlet could guess what was probably meant. I
added a bit of that logic into proxy-logging now as we saw some
errors resulting from this.
Fixes Bug #1012714
Change-Id: I671453eaf3704eab814ff12c4625ba7d749cc7ed