ignore ISABELLE_LINE_EDITOR for code generation

--- a/lib/Tools/codegen	Fri Feb 27 16:05:40 2009 +0100
+++ b/lib/Tools/codegen	Mon Mar 02 08:15:32 2009 +0100
@@ -36,5 +36,6 @@
 THY=$(echo $THY | sed -e 's/\\/\\\\"/g; s/"/\\\"/g')
 ISAR="theory Codegen imports \"$THY\" begin export_code $CMD end"
 
+export ISABELLE_LINE_EDITOR=""
 echo "$ISAR" | "$ISABELLE_TOOL" tty -l "$IMAGE"
 exit ${PIPESTATUS[1]}