Issue 12504 - Added a loop to scan the include_path to allow test classes to be loaded from extension folders when running civix test.
CRM-12504 - StandardTestSuiteLoader - Tweak layout

----------------------------------------
* CRM-12504: Unit Tests cannot be loaded from extension directories due to a particular path expected in PHPUnit_Runner_StandardTestSuiteLoader.php
  http://issues.civicrm.org/jira/browse/CRM-12504