title: Determine if Magento module is enabled
body: <p>What is the best way to determine if a particular module is enabled/active in Magento?  I've tried using <code>class_exists</code> to check if my code has been loaded and parsed by PHP but lately I've noticed its pretty unreliable (returns <code>true</code> even when I delete the module's .xml configuration).</p>
  
  <p>Is there a core function I can call?</p>