Log Message:
Update ruby-shoulda-context to 1.2.2.

* Added factoid about test method names needed to run a single test method
* described_type: no ancestor lookup for constants that don't exist
* Add `require "test/unit"` to README
  The need to require `Test::Unit` in the standard library can be
  non-obvious: #47
* Uses class eval to not lose context
* Refactor to make hound happy