[PATCH] Apache 2.0 Proxy & Windows Update

[Tikka, Sami]

Apache2 proxy seems to drop Content-Length header from replies to HEAD
requests. This is very bad for Microsoft's Windows Update system (and against
HTTP spec). The problem is caused by CONTENT_LENGTH output filter setting
Content-Length header to zero because there is no body data. Later on Apache
removes Content-Length header if it has value 0.

The attached patch fixes the problem in CONTENT_LENGTH output filter by
preventing it from modifying the content length of a reply to HEAD request.

The attached patch is against HEAD of APACHE_2_0_BRANCH as of this morning.