Build system overhaul and spring cleaning.

We'll clear out a load of old cruft:

  * mgLib is going to die, so remove all of the GTK-based tools.  We'll
    rewrite them in Python soon.  Leave the manpages, though.

  * The xwait and xtell tools are going to be combined together into a
    single program with subcommands, so we may as well delete them and
    their manpages.

Fix the email addresses in manpages.

The Debian part of the build system is also refurbished, and based on
CDBS.