Update RSpec to 3.0.0.beta2

Update the RSpec and add some better config to handle mocks.

closes #260 #273 

With this we have some warning from Active Support.

```
$ bundle exec rake
/Users/mauro/.rvm/rubies/ruby-2.1.1/bin/ruby -S rspec ./spec/acceptance/dummy_spec.rb
*

Pending:
  Homepage
    # Temporarily skipped with xit
    # ./spec/acceptance/dummy_spec.rb:5

Finished in 0.02805 seconds
1 example, 0 failures, 1 pending

Deprecation Warnings:

Requiring `rspec/autorun` when running RSpec via the `rspec` command is deprecated. Called from /Users/mauro/.rvm/gems/ruby-2.1.1@pahtest/gems/activesupport-4.0.4/lib/active_support/dependencies.rb:229:in `require'.


If you need more of the backtrace for any of these deprecations to
identify where to make the necessary changes, you can configure
`config.raise_errors_for_deprecations!`, and it will turn the
deprecation warnings into errors, giving you the full backtrace.

1 deprecation warning total

Randomized with seed 41797
```

But to me it is no big deal, new rails probably will solve this.

@fgrehm got no success on use of `config.raise_errors_for_deprecations!` even with this the Active Support error still a warning.