Convert bake tests to compare to files

This results in much more comprehensible tests.

It's easy to cheat and [populate the bake compare folder](https://github.com/AD7six/cakephp/commit/475d82846e6e9267470b03bf013e6fea048c6590) should the bake templates be significantly modified in the future.
Ah.. I was expecting something about the case of `posts`. Yeah the bake template will need updating to fix that.