RAW: provide dummy Isar.main to make tty work gracefully (with ML toplevel);

--- a/src/Pure/mk	Thu Mar 19 18:20:27 2009 +0100
+++ b/src/Pure/mk	Thu Mar 19 19:49:09 2009 +0100
@@ -91,6 +91,7 @@
     -e "val ml_system = \"$ML_SYSTEM\";" \
     -e "val ml_platform = \"$ML_PLATFORM\";" \
     -e "use\"$COMPAT\" handle _ => exit 1;" \
+    -e "structure Isar = struct fun main () = () end;" \
     -q -w RAW_ML_SYSTEM RAW > "$LOG" 2>&1
   RC="$?"
 elif [ -n "$RAW_SESSION" ]; then