updated contributors;

--- a/doc-src/IsarRef/isar-ref.tex	Sun Mar 01 13:48:17 2009 +0100
+++ b/doc-src/IsarRef/isar-ref.tex	Sun Mar 01 14:36:27 2009 +0100
@@ -24,12 +24,13 @@
   With Contributions by
   Clemens Ballarin,
   Stefan Berghofer, \\
+  Timothy Bourke
   Lucas Dixon,
-  Florian Haftmann,
-  Gerwin Klein, \\
+  Florian Haftmann, \\
+  Gerwin Klein,
   Alexander Krauss,
-  Tobias Nipkow,
-  David von Oheimb, \\
+  Tobias Nipkow, \\
+  David von Oheimb,
   Larry Paulson,
   and Sebastian Skalberg
 }