Build-depend on node-less, python-setuptools, and python-nose.

A particular spambayes version is checked at run time, so Depend on that
or get error "pkg_resources.DistributionNotFound: spambayes==1.1b1" .  Note,
this doesn't seem to be popular yet.

Recommend gnupg so it is usually installed along with mailpile, but not
strictly necessary.