Add option to /scripts/pkgacct to keep e-mail configuration

As a web hosting provider, I would like cPanel to add a flag to the pkgacct script that would backup email account configurations and directory structure without backing up the email in those accounts. This has multiple benefits:

• backing up accounts with this flag would complete more quickly
• restoring such a package would rebuild the mail folder directory structure, allowing e-mail to starts working again quickly.
• using this kind of account backup would drastically improve a full server restoration process
• when combined with --skiphomedir you would be given a backup that is just the skeleton of an account, allowing the admin to complete the migration manually