Add DCC support into whom Plus a test for it.
whom: Suppress the separator if no hidden rcpts are present.
Re-added whom(1). This implementation is written from scratch. This new version of whom(1) is quite different to the old one, yet it serves the same purpose: listing the recipients of a message. It still misses the ability to process +folder and msgs arguments. As this implementation is new and not much practically tested, it may change in the future, if flaws appear.