Work with both tar-format.0.2.1 and tar-format.0.3.0

Fixes xapi-project#21

Signed-off-by: David Scott <dave.scott@citrix.com>

Author: David Scott

src/impl.ml

@@ -319,16 +319,11 @@ module TarStream = struct
   }
 
   let make_tar_header prefix counter suffix file_size =
-    Tar.Header.({
-      file_name = Printf.sprintf "%s%08d%s" prefix counter suffix;
-      file_mode = 0o644;
-      user_id = 0;
-      group_id = 0;
-      file_size = Int64.of_int file_size;
-      mod_time = Int64.of_float (Unix.gettimeofday ());
-      link_indicator = Tar.Header.Link.Normal;
-      link_name = ""
-    })      
+    Tar.Header.make
+      ~mod_time:(Int64.of_float (Unix.gettimeofday ()))
+      ~file_mode:0o0644
+      (Printf.sprintf "%s%08d%s" prefix counter suffix)
+      (Int64.of_int file_size)
 end
 
 let stream_tar common c s _ prefix ?(progress = no_progress_bar) () =