Skipping model/concerns folder

In rails models can have "concerns" (a default pattern in rails4) - which help skinny out models and separate common code among them. But if you try to load them you'll get exceptions since they aren't always prefixed with `concerns::` but yet live in the `model/concerns` folder. This causes the call to `constantize` to fail.

There might be a more elegant way to solve this, but here we have a quick and dirty solution.

What do you think?