reflectx: fixes to items reported by megacheck

reflectx/reflect.go

@@ -269,9 +269,7 @@ type typeQueue struct {
 // A copying append that creates a new slice each time.
 func apnd(is []int, i int) []int {
 	x := make([]int, len(is)+1)
-	for p, n := range is {
-		x[p] = n
-	}
+	copy(x, is)
 	x[len(x)-1] = i
 	return x
 }