This patch solves some problems in wget and Firefox, when doing a partial
request (Range:) on a file on a Plan 9 httpd. The Plan 9 httpd does not
send out a Content-Length: when doing so, but these applications expect to
have one and show it directly to the user.

One clause in the HTTP 1.1 RFC says in section 4.4 Message Length:
"For compatibility with HTTP/1.0 applications, HTTP/1.1 requests contain-
ing a message-body MUST include a valid Content-Length header field unless
the server is known to be HTTP/1.1 compliant."

Compliant or not complianet - here is the patch.