src/Pure/System/session.scala

--- a/src/Pure/System/session.scala	Thu Apr 05 13:01:54 2012 +0200
+++ b/src/Pure/System/session.scala	Thu Apr 05 14:14:51 2012 +0200
@@ -296,7 +296,7 @@
     {
       val previous = global_state().history.tip.version
 
-      prover.get.cancel_execution()
+      prover.get.discontinue_execution()
 
       val text_edits = header_edit(name, header) :: edits.map(edit => (name, edit))
       val version = Future.promise[Document.Version]