reflect: add direct call tests to TestMakeFuncVariadic

TestMakeFuncVariadic only called the variadic function via Call and
CallSlice, not via a direct function call.

I thought these tests would fail under gccgo tip, but they don't.  Still seems worth having though.

LGTM=iant
R=golang-codereviews, gobot, iant
CC=golang-codereviews
https://golang.org/cl/152060043

src/reflect/all_test.go

@@ -1543,7 +1543,17 @@ func TestMakeFuncVariadic(t *testing.T) {
 	fv := MakeFunc(TypeOf(fn), func(in []Value) []Value { return in[1:2] })
 	ValueOf(&fn).Elem().Set(fv)
 
-	r := fv.Call([]Value{ValueOf(1), ValueOf(2), ValueOf(3)})[0].Interface().([]int)
+	r := fn(1, 2, 3)
+	if r[0] != 2 || r[1] != 3 {
+		t.Errorf("Call returned [%v, %v]; want 2, 3", r[0], r[1])
+	}
+
+	r = fn(1, []int{2, 3}...)
+	if r[0] != 2 || r[1] != 3 {
+		t.Errorf("Call returned [%v, %v]; want 2, 3", r[0], r[1])
+	}
+
+	r = fv.Call([]Value{ValueOf(1), ValueOf(2), ValueOf(3)})[0].Interface().([]int)
 	if r[0] != 2 || r[1] != 3 {
 		t.Errorf("Call returned [%v, %v]; want 2, 3", r[0], r[1])
 	}
@@ -1552,6 +1562,17 @@ func TestMakeFuncVariadic(t *testing.T) {
 	if r[0] != 2 || r[1] != 3 {
 		t.Errorf("Call returned [%v, %v]; want 2, 3", r[0], r[1])
 	}
+
+	f := fv.Interface().(func(int, ...int) []int)
+
+	r = f(1, 2, 3)
+	if r[0] != 2 || r[1] != 3 {
+		t.Errorf("Call returned [%v, %v]; want 2, 3", r[0], r[1])
+	}
+	r = f(1, []int{2, 3}...)
+	if r[0] != 2 || r[1] != 3 {
+		t.Errorf("Call returned [%v, %v]; want 2, 3", r[0], r[1])
+	}
 }
 
 type Point struct {