code review 1453041: big: bug fix for Quo aliasing problem

src/pkg/big/rat.go

Index: src/pkg/big/rat.go
===================================================================
--- a/src/pkg/big/rat.go
+++ b/src/pkg/big/rat.go
@@ -160,9 +160,11 @@
 	if len(y.a.abs) == 0 {
 		panic("division by zero")
 	}
-	z.a.abs = z.a.abs.mul(x.a.abs, y.b)
-	z.b = z.b.mul(x.b, y.a.abs)
-	z.a.neg = x.a.neg != y.a.neg
+	a := mulNat(&x.a, y.b)
+	b := mulNat(&y.a, x.b)
+	z.a.abs = a.abs
+	z.b = b.abs
+	z.a.neg = a.neg != b.neg
 	return z.norm()
 }