mikel/mail — pull request #693 by banyan (2014-03-27 18:40:05+00:00)
Title: Makes RSpec3 compatible

`negative_failure_message` is replaced with `failure_message_when_negated`.
Remain `negative_failure_message` for the backwards compat.

It's a similar issue of capybara: https://github.com/jnicklas/capybara/pull/1219