In the past the port was specified by adding ":port" after the host name. However, this is not very discoverable and doesn't seem to be working with the latest PHPMailer version. The aim of this issue is to do some clean up relating to PHPMailer / SMTP integration including:

1. Add $g_smtp_port configuration option.
2. Update docbook documentation including the addition of documentation for $g_smtp_connection_mode and $g_smtp_port.
3. Use constants for PHPMailer methods rather than 0, 1, and 2.

This should also allow easy use of gmail as the smtp server. Here are the steps:

1. Set $g_phpMailer_method to PHPMAILER_METHOD_SMTP
2. Set $g_from_email to 'username@gmail.com'
3. Set $g_from_name to 'Mantis Bug Tracker'
4. Set $g_smtp_host to 'smtp.gmail.com'
5. Set $g_smtp_port to 465
6. Set $g_smtp_connection_mode to 'ssl'
7. Set $g_smtp_username to 'username@gmail.com'
8. Set $g_smtp_password to 'your_secret_password'