eager_load_chewy! conflicts with rails autoloading

Bit of a weird one this, perhaps I'm doing something I shouldn't....

I've added a ```concerns``` directory to ```/app/chewy``` because I have some duplication across index definitions.  I then include these modules into the index definitions, e.g.:

```ruby
class AccountsIndex < Chewy::Index
  define_type AccountX.includes(:associationX) do
    include CommonIndexStuff

    field :fieldX
  end

  define_type AccountY.includes(:associationY) do
    include CommonIndexStuff

    field :fieldY
  end
end
```

When I run ```rake chewy:reset```, I get ```ActiveSupport::Concern::MultipleIncludedBlocks: Cannot define multiple 'included' blocks for a Concern``` because the ```eager_load_chewy!``` method in ```chewy.rake``` first causes Rails to autoload the ```CommonIndexStuff``` module, and then explicitly ```require```s it again. 

There are three ways to solve this:

1. Only eager load index definition files, using the convention that all index definitions are in files that end with the suffix ```_index.rb```.
2. Use ```require_dependency``` rather than ```require``` in ```eager_load_chewy!```, because that lets Rails autoloading mechanism ignore the second attempt to load that file.
3. Move all non-index definition files out of ```/app/chewy``` and into another directory like ```/lib/chewy```.

I don't like option 3, because that just seems cryptic and annoying. Out of options 1 and 2, I've plumped for 1 because 2 felt like unnecessary coupling to Rails.

Thoughts?