go.crypto/bn256: updates tests in light of b2b2ae1f5140.

https://golang.org/cl/6850091 fixed the bug in question.
This change updates the tests so that they are broken without
that change.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/6846091

bn256/bn256_test.go

@@ -273,12 +273,12 @@ func TestTripartiteDiffieHellman(t *testing.T) {
 	b, _ := rand.Int(rand.Reader, Order)
 	c, _ := rand.Int(rand.Reader, Order)
 
-	pa := new(G1).ScalarBaseMult(a)
-	qa := new(G2).ScalarBaseMult(a)
-	pb := new(G1).ScalarBaseMult(b)
-	qb := new(G2).ScalarBaseMult(b)
-	pc := new(G1).ScalarBaseMult(c)
-	qc := new(G2).ScalarBaseMult(c)
+	pa, _ := new(G1).Unmarshal(new(G1).ScalarBaseMult(a).Marshal())
+	qa, _ := new(G2).Unmarshal(new(G2).ScalarBaseMult(a).Marshal())
+	pb, _ := new(G1).Unmarshal(new(G1).ScalarBaseMult(b).Marshal())
+	qb, _ := new(G2).Unmarshal(new(G2).ScalarBaseMult(b).Marshal())
+	pc, _ := new(G1).Unmarshal(new(G1).ScalarBaseMult(c).Marshal())
+	qc, _ := new(G2).Unmarshal(new(G2).ScalarBaseMult(c).Marshal())
 
 	k1 := Pair(pb, qc)
 	k1.ScalarMult(k1, a)