Require additional rspec dependencies for Rspec 2.14.x

In a Rails app, I recently updated to Rspec 2.14.4, and remockable stopped working (`undefined method `define' for RSpec::Matchers:Module (NoMethodError)`). Seems like the reason is because Rspec now is autoloading `RSpec::Mocks` and `RSpec::Matchers` when they are called, but remockable isn't picking this up. To deal with it I explicitely require those libraries.