Mailman sort patch

When using sendmail, you can see suboptimal performance. While there are some tweaks that can be done, eg: adjusting SMTP_MAX_RCPTS, you can also see a significant performance gain by sorting by domain.

I have been using this patch privately since at least 2004 and wanted to share it to be included in future releases if feasible.

There is a second part of it that also adjusts the chunk map which can either be incorporated or excluded as well.

This will put folks who are @gmail.com all together when handed to sendmail (for example) instead of interspersed in some other ordering.

One can argue the MTA should do this, but this is a light-weight approach to optimally utilize resources if the MTA doesn't handle it properly.