Add test

Author: odersky

tests/pos/combine.scala

@@ -0,0 +1,10 @@
+trait Semigroup[A] {
+  def (x: A) combine (y: A): A
+}
+delegate for Semigroup[Int] = ???
+delegate [A, B] for Semigroup[(A, B)] given Semigroup[A], Semigroup[B] = ???
+object Test extends App {
+  ((1, 1)) combine ((2, 2)) // doesn't compile
+  ((1, 1): (Int, Int)) combine (2, 2) // compiles
+  //the error that compiler spat out was "value combine is not a member of ((Int, Int)) => (Int, Int)". what's
+}