Do not chunk responses carrying a Content-Range header.

When Squid forwards a response with a Content-Range header,
ClientSocketContext::socketState() detects the end of the response range(s)
and returns STREAM_*COMPLETE to ClientSocketContext::writeComplete().
The latter thinks that the writing of the response to the client must be
over and calls keepaliveNextRequest() instead of writing the last-chunk 
(if any). If the to-client response was chunked, the client gets stuck 
waiting for that missing last-chunk.

The multipart Range request case was already excluded from chunking (or it
would probably suffer from the same problem). With this change, no
Content-Range responses will be chunked.

N.B. Some servers send Content-Range responses to basic GET requests
without a Range header, so the problem affects more than just Range requests.

TODO: A proper fix would be to rewrite ClientSocketContext::writeComplete()
and other code so that it does not mix internal ClientStream completion with
[possibly chunk-encoded] writing completion. This should probably be done
along with fixing ClientSocketContext::socketState() and other state-checking
code to ignore to-client persistence (flags.proxy_keepalive), which is not
related to the internal ClientStream state.

=== modified file 'src/client_side_reply.cc'
--- src/client_side_reply.cc	2012-08-14 11:53:07 +0000
+++ src/client_side_reply.cc	2012-08-24 03:49:33 +0000
@@ -1448,9 +1448,13 @@
                       getMyHostname(), getMyPort());
 
 #endif
 
+    // chunking a Content-Range response may not violate specs, but our
+    // ClientSocketContext::writeComplete() confuses the end of ClientStream
+    // with the end of to-client writing and may quit before writing last-chunk
     const bool maySendChunkedReply = !request->multipartRangeRequest() &&
+                                     !reply->content_range &&
                                      reply->sline.protocol == AnyP::PROTO_HTTP && // response is HTTP
                                      (request->http_ver >= HttpVersion(1, 1));
 
     /* Check whether we should send keep-alive */