added toplevel isabelle package -- reduce warnings with scala-2.9.0.final;

--- a/src/Pure/build-jars	Thu May 12 16:42:57 2011 +0200
+++ b/src/Pure/build-jars	Thu May 12 16:46:21 2011 +0200
@@ -63,6 +63,7 @@
   Thy/thy_header.scala
   Thy/thy_syntax.scala
   library.scala
+  package.scala
 )
 
 TARGET_DIR="$ISABELLE_HOME/lib/classes"

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/package.scala	Thu May 12 16:46:21 2011 +0200
@@ -0,0 +1,11 @@
+/*  Title:      Pure/package.scala
+    Author:     Makarius
+
+Toplevel isabelle package.
+*/
+
+package object isabelle
+{
+  def error(message: String): Nothing = throw new RuntimeException(message)
+}
+