more general workaround for failed sessions (again, see also 2edb89630a80, ed7b5cd3a7f2);

--- a/src/Pure/Admin/build_status.scala	Sun May 21 23:10:39 2017 +0200
+++ b/src/Pure/Admin/build_status.scala	Sun May 21 23:41:46 2017 +0200
@@ -166,7 +166,7 @@
             {
               val threads1 =
                 res.string(Build_Log.Settings.ISABELLE_BUILD_OPTIONS) match {
-                  case Threads_Option(Value.Int(i)) if session_name == "Pure" => i
+                  case Threads_Option(Value.Int(i)) => i
                   case _ => 1
                 }
               val threads2 = res.get_int(Build_Log.Data.threads).getOrElse(1)