This is a backward-compatible rewrite of the mailbox module to support
mailbox modification and mailbox-format-specific message attributes.

It's being written as part of Google's Summer of Code program[1] by
Gregory K. Johnson with mentoring from A.M. Kuchling. Greg's project
proposal[2] is available online, and summaries[3] of all of the accepted
proposals for Python are on the Python Wiki.

[1] http://code.google.com/summerofcode.html
[2] http://gkj.freeshell.org/summer_of_code/
[3] http://wiki.python.org/moin/SummerOfCode