rspec/rspec-expectations — pull request #539 by dtaniwaki (2014-04-26 09:17:26+00:00)
Title: Pass matcher to message proc

Hi,

I wanted to do like this.
```rb
expect(something).to eq('other thing'), lambda { |matcher| "\n[step 1]\n#{matcher.failure_message}" }
```

However, the failure message caller object doesn't pass the matcher so I can't use it in the proc. Could you consider to merge this feature?