title: Dependency Isolation and Declaration in PHP
body: <p>What's the best way to achieve complete <a href="http://12factor.net/dependencies" rel="noreferrer">dependency declaration and isolation</a> in a PHP web app? I already know about <a href="http://getcomposer.org/" rel="noreferrer">Composer</a>, but that's only the declaration part and I don't think it goes far enough. I'd like to include as much of the following as I can: PHP extensions (e.g. mcrypt, imagick, apc), the php.ini config and configs for extensions, PECL packages, and ideally even my Apache config files. Is there something like Ruby's <code>bundle exec</code> for PHP?</p>