The proxy_logging middleware was asserting that the response contained
either a Content-Length header or a Transfer-Encoding header. If not,
it would either add one (if app_iter was a list) or blow up
(otherwise). This blowing up is observable on a GET request to a
manifest object that references more than
swift.common.constraints.CONTAINER_LISTING_LIMIT segments.
If a response makes it up to eventlet.wsgi without a Content-Length
header, then a "Transfer-Encoding: chunked" header is automatically
stuffed into the response by eventlet. Therefore, it's not an error
for a response to not have a Content-Length header, and proxy_logging
should just let it happen.
Fixes bug 1078113.
Change-Id: I3751a8ae14dc68bab546f2746b61267a5115e252
a78b2d5f46