Merge r5189: Document HTTP Range

git-svn-id: http://www.varnish-cache.org/svn/branches/2.1@5347 d4fa192b-c00b-0410-8231-f00ffab90ce4

doc/sphinx/reference/varnishd.rst

@@ -484,6 +484,12 @@ http_headers
       This space is preallocated in sessions and workthreads only objects allocate only space for the headers
       they store.
 
+http_range
+      Default: off
+      
+      Enables experimental support for the HTTP range header, enabling Varnish to serve parts of 
+      an object to a client. However, Varnish will request the whole object from the backend server.
+
 listen_address
       Default: :80
       Flags: must_restart