Remove deprecation warning for Rspec 3.0.0 in have_received matcher

Those deprecation warnings are really annoying and Rspec 3 is coming rather sooner than later - more and more people are using it right now without the stable release.

This pull request is using the new `failure_message` and `failure_message_when_negated` and aliasing the deprecated `failure_message_for_should` and `failure_message_for_should_not` for backward compatibility.