Corrects logic to only apply default filename in **all** cases where none provided.
CakeSchema naming fallback.

Abstracts the `require_once` of the schema file so it can be done twice. The added second call is a fallback for the previous APP_DIR-based naming to provide backwards compatibility.

Removes now-obsolete CakeSchema tests that involved `Configure::read('App.dir')`. The CakeSchema::name is now always static (and predictable) in the default case.