more general prover termination dialog, which might indicate undetected failure or just ML "exit 0";

--- a/src/Tools/jEdit/src/plugin.scala	Thu Jan 10 19:07:44 2013 +0100
+++ b/src/Tools/jEdit/src/plugin.scala	Thu Jan 10 19:53:38 2013 +0100
@@ -189,9 +189,9 @@
       react {
         case phase: Session.Phase =>
           phase match {
-            case Session.Failed =>
+            case Session.Inactive | Session.Failed =>
               Swing_Thread.later {
-                Library.error_dialog(jEdit.getActiveView, "Prover process failure",
+                Library.error_dialog(jEdit.getActiveView, "Prover process terminated",
                     "Isabelle Syslog", Library.scrollable_text(PIDE.session.current_syslog()))
               }