mail/mimedefang: 2.75 -> 2.78

Changes:

• Fix code that coalesces multiparts into single-parts so that it does not break DKIM signing. Fix is courtesy of Peter Nagel.
• Change old author's name to "Dianne Skoll" in many places.
• Add "All / Summary" button to watch-multiple-mimedefangs.tcl
• Add a filter_wrapup callback. This permits header modifications, but not body modifications. It has access to the final (possibly modified) message, so is the ideal place to do DKIM-signing.
• Remove all function prototypes from mimedefang.pl.in as per current Perl5 best practices.

Submitted by: Mikhail Tsatsenko <m.tsatsenko@gmail.com> (maintainer)