Configurable removal of MIME sections

[Lniles]

This patch adds a Handler that scans each message for
MIME content, removing those sections whose mime types
match one of a list of regexps. multipart/alternative
sections are replaced by the first non-empty
component, and multipart/mixed sections that wrap only
single sections after other processing are replaced by
their contents.
This is a patch against 2.1alpha4.

[http://sourceforge.net/tracker/index.php?func=detail&aid=501199&group_id=103&atid=300103]

[Barry Warsaw (barry)]

I think this is quite interesting, and while I'd need to
make some changes to it, I think it's a decent approach that
many will like to have in MM2.1. Your contribution is large
enough that I'd need you to assign copyright on it to the
FSF. Would you be willing to do that if I got the right
forms sent to you?

[Lniles (lniles)]

Not a problem, I'm happy to assign the copyright.

[Barry Warsaw (barry)]

Les, let's go ahead and get you signed off on this patch.
I've spent a few hours taking another look at it, and I
although I've hacked heavily on MimeDel.py, I believe what I
have is good enough for MM2.1. Watch for a follow up
through regular email.