use LONG rather than INT to represent the C datatype size_t

--- a/src/Pure/General/sha1_polyml.ML	Tue Mar 23 10:07:39 2010 -0700
+++ b/src/Pure/General/sha1_polyml.ML	Tue Mar 23 20:46:08 2010 +0100
@@ -24,7 +24,7 @@
     val digest = CInterface.alloc 20 CInterface.Cchar;
     val _ =
       CInterface.call3 (CInterface.get_sym (File.platform_path lib_path) "sha1_buffer")
-        (CInterface.STRING, CInterface.INT, CInterface.POINTER)
+        (CInterface.STRING, CInterface.LONG, CInterface.POINTER)
         CInterface.POINTER (str, size str, CInterface.address digest);
   in fold (suffix o hex_string digest) (0 upto 19) "" end;