The purpose is to make code more readable.

Follow up on fix for issue #14447.

Version 5.2.1 (January 16, 2012)
* Closed several bugs
* Performance improvements
* MsgHTML() now returns the message as required.
* New method: GetSentMIMEMessage() (returns full copy of sent message)

Version 5.2 (July 19, 2011)
* protected MIME body and header
* better DKIM DNS Resource Record support
* better aly handling
* htmlfilter class added to extras
* moved to Apache Extras

Fixes #12562

Prior to this, several e-mail related events were not reported at all,
making troubleshooting of issues difficult. The following cases are now
logged:

 * sending of queued messages (email_send_all)
 * errors thrown by PHPMailer
 * reminder emails (email_bug_reminder) - fixes #9368
 * deletion of records from the email queue

In addition, admin/email_queue.php was modified to print a formatted
date instead of a numeric timestamp.

PHPMailer uses filter_var() to check for an e-mail validity; this
function treats single-domain e-mail addresses (e.g. user@localhost) as
invalid. However, Mantis API function email_is_valid() relies on a
custom regex to validate e-mails, which does accept such addresses. As a
consequence, we accept addresses to which we are unable to send
messages.

To avoid this problem, we now rely on PHPMailer::ValidateAddress()
method to ensure that any email we store can be sent PHPMailer.

Prior to this, function email_is_valid() always returned true when
$g_use_ldap_email = ON, even if $g_login_method != LDAP.

Even though this is not an usual case (when not using LDAP, the other
LDAP-related configuration options should be left to their default
values), this causes the actual validation to be skipped which could
lead to email sending errors.

Fixes #14632