Treat truncated HTTP requests as errors.

Treat truncated HTTP requests as errors.

We detect such prematurely ended request when there's a Content-Length
greater than the body we got. A strict comparison would easily fail
when there was a content encoding layer, but hopefully we won't hit
a compressed request _larger_ than the original content.

See http://thread.gmane.org/gmane.org.wikimedia.mediawiki/39622
for breakage caused by truncated HTTP replies.

Change-Id: I71418424730d46a781bde5cbfda8038457ec79c5