Fix test/include.test.js

In my pull request for jugglindb-redis (see https://github.com/jugglingdb/redis-adapter/pull/3), I noticed that the include.test.js is not properly testing the cached relations for included models.

For example:

``` javascript
u.__cachedRelations.should.have.property('posts');
u.__cachedRelations.posts.forEach(function(p) {
p.userId.should.equal(u.id);
});
```

`p.userId.should.equal(u.id)` will never be checked if `u.__cachedRelations.posts == []`, thus the test will pass. Without comparing the query results to the mocked models, the tests can't check if the cached relations _should_ contain results.

I will submit a pull request when I find time, but I thought I should point it out, as many adapters could be erroneously passing the include tests.