added try_result;

--- a/src/Pure/Tools/isabelle_process.scala	Sun Aug 24 21:15:48 2008 +0200
+++ b/src/Pure/Tools/isabelle_process.scala	Mon Aug 25 16:52:11 2008 +0200
@@ -111,6 +111,11 @@
 
   def get_result() = results.take
 
+  def try_result() = {
+    val res = results.poll
+    if (res != null) Some(res) else None
+  }
+
 
   /* signals */