[allow coersions on arbitrary subexpressions
John Meacham <john@repetae.net>**20060303042203] hunk ./E/FromHs.hs 512
+    cExpr (HsAsPat n' e) = do
+        e <- cExpr e
+        cc <- asks ceCoerce
+        case Map.lookup (toName Val n') cc of
+            Nothing -> return e
+            Just c -> applyCoersion c e