max_threads_value always 1 for dummy version;

--- a/src/Pure/ML-Systems/multithreading.ML	Thu Oct 02 14:22:44 2008 +0200
+++ b/src/Pure/ML-Systems/multithreading.ML	Thu Oct 02 14:22:45 2008 +0200
@@ -37,7 +37,7 @@
 
 val available = false;
 val max_threads = ref (1: int);
-fun max_threads_value () = Int.max (! max_threads, 1);
+fun max_threads_value () = 1: int;
 
 val no_interrupts =
   [Thread.EnableBroadcastInterrupt false, Thread.InterruptState Thread.InterruptDefer];