more quotes;

--- a/src/HOL/Tools/Nitpick/lib/Tools/nitrox	Thu Jul 14 22:53:43 2011 +0200
+++ b/src/HOL/Tools/Nitpick/lib/Tools/nitrox	Thu Jul 14 23:05:25 2011 +0200
@@ -24,5 +24,5 @@
 do
   echo "theory $SCRATCH imports \"Nitpick\" begin ML {* Nitrox.pick_nits_in_fof_file \"$FILE\" *} end;" \
     > /tmp/$SCRATCH.thy
-  $ISABELLE_PROCESS -e "use_thy \"/tmp/$SCRATCH\"; exit 1;"
+  "$ISABELLE_PROCESS" -e "use_thy \"/tmp/$SCRATCH\"; exit 1;"
 done