Why are all these aliased to `setup_expectation`?

* `setup_allowance` is overriden below.
* The negative ones (`does_not_match` and `setup_negative_expectation`) seem wrong to be the same thing as the positive case.

Actually, I'm not sure this should support the negative case at all...what would this mean?

``` ruby
expect(object).not_to receive_messages(foo: 3, bar: 25)
```

It's confusing since return values don't make sense for the negative case.  Would be good to spec this, of course.