Upgrade PHPMailer from 5.02 to 5.1

Changes:

Version 5.1 (October 20, 2009)

• fixed filename issue with AddStringAttachment (thanks to Tony)
• fixed "SingleTo" property, now works with Senmail, Qmail, and SMTP in
  addition to PHP mail()
• added DKIM digital signing functionality
  New properties:
  • DKIM_domain (sets the domain name)
  • DKIM_private (holds DKIM private key)
  • DKIM_passphrase (holds your DKIM passphrase)
  • DKIM_selector (holds the DKIM "selector")
  • DKIM_identity (holds the identifying email address)
• added callback function support
  • callback function parameters include:
    result, to, cc, bcc, subject and body
  • see the test/test_callback.php file for usage.
• added "auto" identity functionality
  • can automatically add:
  • Return-path (if Sender not set)
  • Reply-To (if ReplyTo not set)
  • can be disabled:
  • $mail->SetFrom('yourname@yourdomain.com','First Last',false);
  • or by adding the $mail->Sender and/or $mail->ReplyTo properties
    Note: "auto" identity added to help with emails ending up in spam
    or junk boxes because of missing headers