src/Pure/General/exn.scala

--- a/src/Pure/General/exn.scala	Wed Mar 15 21:52:04 2017 +0100
+++ b/src/Pure/General/exn.scala	Thu Mar 16 11:25:09 2017 +0100
@@ -20,7 +20,7 @@
       }
     override def hashCode: Int = message.hashCode
 
-    override def toString: String = Output.error_text(message)
+    override def toString: String = "\n" + Output.error_text(message)
   }
 
   object ERROR