Move spec_helper to rails_helper.

The first step to providing the ability to only include the necessary
parts of Rails to keep specs happy. By separating general RSpec
configuration from the Rails specific configuration, any specs which
don't need rails, can load a standard helper.

- Update Rails generators to reference the new helper file
- Fix specs for the generators
- Let cukes know about `rails_helper`
Incorporate rspec-core's project initialization.

The Rails centric helper is now `rails_helper`. Leverage the standard
RSpec configuration for creating basic configurations for `.rspec` and
`spec_helper`. This also keeps us in-sync with any future changes.

- Fix #1029
Remove duplicate settings between the helpers.

The `rails_helper` only needs to be concerned with rspec-rails specific
configurations. Any general configuration is handled by `spec_helper`.
Note change of `spec_helper` and `rails_helper`.
Merge pull request #1049 from rspec/rails-helper

Separate RSpec and Rails specific configurations