First attempt at an `rspec-rails` configuration helper

Hi, I've given the `rspec-rails` config a go, basically by copying the `spec` config and changing which helper file gets loaded (`rails_helper.rb` instead of `spec_helper.rb`).

I noticed that the glob patterns double up, as both `spec` and `rspec-rails` are loaded by default, since there is a `spec_helper.rb` *and* `rails_helper.rb` present in the spec directory. I'm not sure if this is a problem?

One thing that this raised is that there is a problem on line 30 of the `driver.rb`. It was expanding an array of glob patterns, but [according to the documentation for Dir#glob](http://www.ruby-doc.org/core-1.9.3/Dir.html#method-c-glob), the first argument should be a string or an array, but not multiple strings. The upshot of this is that running all test files would throw this error. The very simple fix is to remove the array expansion, and it all works.

I also noticed a problem with rails 4 and the rails config helper, but I'll submit another PR after this.

Please make any suggestions as to what is needed/not needed for this PR to make it in - you know much more than me about how the configuration helpers should work!