Curl_proxyCONNECT: count received headers

Proxy servers tend to add their own headers at the beginning of
responses. The size of these headers was not taken into account by
CURLINFO_HEADER_SIZE before this change.

Bug: http://curl.haxx.se/bug/view.cgi?id=1204

lib/http_proxy.c

@@ -356,6 +356,10 @@ CURLcode Curl_proxyCONNECT(struct connectdata *conn,
 
                   result = Curl_client_write(conn, writetype, line_start,
                                              perline);
+
+                  data->info.header_size += (long)perline;
+                  data->req.headerbytecount += (long)perline;
+
                   if(result)
                     return result;