Issues/677 require regexp validator bug

For more information (see the actual Github [issue](https://github.com/intridea/grape/issues/677)) that this describes.

Based on the failing specs in this PR I think the way validation errors are handled may be able to be simplified which solves the original issue I had (see [this comment](https://github.com/intridea/grape/issues/677#issuecomment-53008917)). If that's the case then this code here can be even further simplified (and likely most of it deleted).

If that's not the case then I will continue exploring the validation chain logic and update the PR to intelligently group validation errors that must run together and allow others to be short-circuited.