[make slottypes check for free variables before substitution
John Meacham <john@repetae.net>**20061006055801] hunk ./DataConstructors.hs 489
-    sub = substMap'' $ fromDistinctAscList [ (i,Just sl) | sl <- xs | i <- [2,4..] ]
+    sub = substMap $ fromDistinctAscList [ (i,sl) | sl <- xs | i <- [2,4..] ]