Sequence containment does not work in triggers

The following trivial program does not verify:

```
method wow(s: Seq[Int])
  requires forall i: Int :: {i in s} i in s == i > 5
{
    assert 7 in s
}
```

The problem is that the trigger is translated using the function ``Seq#ContainsTrigger``, but the assertion uses the function ``Seq#Contains``, and the two are not connected anywhere in the sequence axiomatization.