Provide buildd as separate Debian package buildd, use nail instead of mutt in buildd...

Provide buildd as separate Debian package buildd, use nail instead of mutt in buildd for sending mails.

Recent Mutt versions introduced an annoying cmdline behaviour change
in a patch version upgrade (1.5.x->1.5.y) which breaks sending mails
from the cmdline when you've to add several attachments at once
and want to stay backward and forward compatible.
See http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=539276
for further details.
Therefore get rid of mutt and use nail for sending mails instead.