accomodate old version of "tail", e.g. on sunbroy2;

--- a/lib/Tools/usedir	Wed Oct 14 16:08:51 2009 +0200
+++ b/lib/Tools/usedir	Wed Oct 14 16:39:35 2009 +0200
@@ -262,7 +262,7 @@
 else
   { echo "$ITEM FAILED";
     echo "(see also $LOG)";
-    echo; tail -n 20 "$LOG"; echo; } >&2
+    echo; tail -20 "$LOG"; echo; } >&2
 fi
 
 exit "$RC"