[xoopsmailer] add class method "getVar($key)"
[user] add delegate points before xoopsmailer->send() with `xoopsmailer`

- sample preload (html/preload/UserPreSendMail.class.php)
```php
<?php

class UserPreSendMail extends XCube_ActionFilter
{
	function postFilter() {
		$this->mRoot->mDelegateManager->add('Legacy.Event.RegistUser.SendMail'
, array($this ,'preSendMail'));
	}
	
	function preSendMail(&$mailer, $action) {

		/* COMMON PROCESS */
		
		/* EDIT SUBJECT */
		//$subject = $mailer->getVar('subject');
		//$mailer->setSubject('['.$action.'] ' . $subject);

		/* CHANGE MAIL FROM */
		//$mailer->setFromEmail('example@example.com');
		//$mailer->setFromName('XOOPS Cube Legacy Site');


		/* PROCESS OF EACH ACTION */

		switch($action) {
			case 'LostPass1' :
				break;
			case 'LostPass2' :
				break;
			case 'Activated' :
				break;
			case 'Register' :
				/* CHANGE TEMPLATE */
				//$mailer->setTemplate('register_custom.tpl');
				break;
			case 'AdminActivate' :
				break;
			case 'Notify' :
				break;
		}
	}
}
```
Merge pull request #107 from XoopsX/registuser_mail_delegate

[user] add delegate points before xoopsmailer->send() with `xoopsmailer`