bug reported by nelson

BUGS

@@ -52,4 +52,7 @@ ide.c: synchronous disk write -> polling disk write.  search for
 fs.c: split all name operations off in name.c?  (starting with namei but move 
       wdir keep in fs.c)
 
+      unlink . and .. should be disallowed
+
 ls.c: apply tim's patch
+