joomla: ensure we don't reset include paths unnecessarily

the civicrm user plugin for joomla takes care of resetting system navigation menu cache when users are created/updated/deleted. however, we shouldn't be including the settings file if that plugin is triggered from a civicrm action, as it results in the include paths being reset with core files preceding override files.

the attached file corrects this.
i'm attaching the full file rather than a patch because I refactored for the new code standards and pretty much the entire file was impacted.