paraphrase works a little better now ; added examples/paraphrase for testing

src/GF/Command/TreeOperations.hs

@@ -25,7 +25,7 @@ allTreeOps pgf = [
    ("compute",("compute by using semantic definitions (def)",
       map (compute pgf))),
    ("paraphrase",("paraphrase by using semantic definitions (def)",
-      concatMap (paraphrase pgf))),
+      nub . concatMap (paraphrase pgf))),
    ("smallest",("sort trees from smallest to largest, in number of nodes",
       smallest)),
    ("typecheck",("type check and solve metavariables; reject if incorrect",