it's a lot easier for adding new translations to think:
is it for the end user?
use 'cake' as the domain
is it for the developer
use 'cake_dev' as the domain
is it for the console
use 'cake_console' as the domain
also neatly avoids the "this message is an error, and it's in
cake_developer, why?" - question (because cake_error was intended for
anything which is used in trigger_error/exceptions, not a variable named
$error
