constructor: allow default logic;

--- a/lib/classes/isabelle/IsabelleDemo.java	Sat Dec 15 23:55:33 2007 +0100
+++ b/lib/classes/isabelle/IsabelleDemo.java	Sun Dec 16 13:05:07 2007 +0100
@@ -43,4 +43,8 @@
             }
         }).start();
     }
+    
+    public IsabelleDemo() throws IsabelleProcessException {
+        this(null);
+    }
 }