Predef.iterable2ordered does not define an ordering

The code
```scala
package test;

object Test {
  def main(args : Array[String]) : Unit = {
    val l1 = List(1,2,3)
    val l2 = List(1,2,3,4)
    Console.println("l1 compare l2 = " + (l1 compare l2))
    Console.println("l2 compare l1 = " + (l2 compare l1))
  }
}
```
produces this inconsistent output:

```scala
l1 compare l2 = 0
l2 compare l1 = 1
```