Match matchers on diffing messages

[dorner]

Currently, Deimos::TestHelpers tries to be smart about reporting the diff between the closest message sent and the reported one. However, in its matching and reporting, it treats matchers as a value rather than something to match against a value - i.e. anything is always treated as different from the other hash rather than the same.

See if we can make this smarter so our error messages are more useful and there isn't a lot of noise about AnyArgMatcher being different from the given value.