composer/composer — pull request #1297 by simensen (2012-11-07 17:37:58+00:00)
Title: Play nicely with external software already using Composer autoloader

Check to see if ComposerAutoloaderInit already exists. If it does, get the loader from there. Otherwise, require the autoload_real.php as before.

Primary use case is phpunit. If phpunit is installed globally via Composer it is not able to be used to run on a project that also uses Composer.