It seems that aliasing is used only in Capybara's own specs. Thus I think this code should be placed somewhere in `spec` folder (I haven't looked yet where it can be placed).

I think it's a bit strange that if a user uses RSpec `2.14.5` he will get `be_truthy` undefined if he doesn't `require 'capybara/rspec'` but defined if he does `require 'capybara/rspec'`