CakePHP comes by default with two “vendors” folders for third-party libraries: one is in the root folder of the cake distribution (for libraries used by multiple applications), and the other is in the “app” folder (for application-specific libraries).
Thanks to changeset 6414 it is now possible to define additional “vendors” folders in app/config/bootstrap.php:
$vendorPaths = array('<path to additional vendors folder>');
If you want to use a file from such an alternative “vendors” folder you have to include it with
App::import('vendor', '<filename without PHP file extension>');
The traditional way — using the vendor() function —
doesn’t work yet has been deprecated according to comments in tickets.