integrate visualfsharp master (8)

Author: dsyme

src/fsharp/tast.fs

@@ -40,7 +40,7 @@ type Stamp = int64
 
 /// Unique name generator for stamps attached to to val_specs, tycon_specs etc.
 //++GLOBAL MUTABLE STATE
-let newStamp = let mutable i = 0L in fun () -> System.Threading.Interlocked.Increment(&i)
+let newStamp = let i = ref 0L in fun () -> System.Threading.Interlocked.Increment(i)
 
 /// A global generator of compiler generated names
 // ++GLOBAL MUTABLE STATE