avoid reference to theory Ferrack altogether

--- a/doc-src/Codegen/Thy/Evaluation.thy	Thu Sep 02 16:41:44 2010 +0200
+++ b/doc-src/Codegen/Thy/Evaluation.thy	Thu Sep 02 16:42:19 2010 +0200
@@ -96,7 +96,7 @@
   allows to use pattern matching on constructors stemming from compiled
   @{text "datatypes"}.
 
-  For a less simplistic example, theory @{theory Ferrack} is
+  For a less simplistic example, theory @{text Ferrack} is
   a good reference.
 *}