implement translation behavior default locale

Unless explicitly overriden, the behavior now reads I18n::defaultLocale() to find the locale to return translations in.

Bundled with this change set is adding support to the translate behavior
for unhydrated result sets

Closes #4509

Ref #4660 
Ah there she goes, thanks. In my bootstrap I had `Locale::setDefault('en_us');` and my values without that are:
```
var_dump(Locale::getDefault()); string(11) "en_US_POSIX"
var_dump(ini_get('intl.default_locale')); string(0) ""
```

Setting that from Cake's I18n class worked.