Added call to update-entity-headers, so that all response entities

will get updated before writing out the response, not only those that
happened to be generated via the access-resource standard method.
This might lead to redundant calls to update-entity-headers, which
might be costly, so maybe some form of last-updated time-stamp should
be kept so that update-entity-headers isn't called more than once a
second.

This fixes the problem we had with Netscape's Proxy-Server:  Since
update-entity-headers wasn't called on e.g. redirector-resource
responses, those didn't contain content-length headers.  This
triggered a bug in Netscape's Proxy-Server (version 3.5 at least),
which kept the connection open even after the explicit close by
CLASH.

src/main/messages.cl

@@ -380,6 +380,7 @@ used to call `reinitialize-instance'."))
     (set-cookie "Set-Cookie"
       (format stream "~:{~A~@[=~A~]~^;~:}" set-cookie)))
   (when (slot-boundp message 'entity)
+    (update-entity-headers (http-message-entity message))
     (render-entity-headers (http-message-entity message) stream)
     (http-terpri stream)
     (unless (or (= (response-status-code message) +HTTP-Code-Not-Modified+)