Merge branch 'tree-diff-option' into 'master'

Remove the Semi.Option instance of ToExpr

See merge request ghc/head.hackage!156

patches/tree-diff-0.2.patch

+diff --git a/src/Data/TreeDiff/Class.hs b/src/Data/TreeDiff/Class.hs
+index 79f928c..03b5f01 100644
+--- a/src/Data/TreeDiff/Class.hs
++++ b/src/Data/TreeDiff/Class.hs
+@@ -375,8 +375,6 @@ instance ToExpr a => ToExpr (Mon.First a) where
+ instance ToExpr a => ToExpr (Mon.Last a) where
+ 
+ -- ...
+-instance ToExpr a => ToExpr (Semi.Option a) where
+-    toExpr (Semi.Option x) = App "Option" [toExpr x]
+ instance ToExpr a => ToExpr (Semi.Min a) where
+     toExpr (Semi.Min x) = App "Min" [toExpr x]
+ instance ToExpr a => ToExpr (Semi.Max a) where