Generalize the packge building scripts to be able to be run on more than
one 'head' node, rather than just pointyhat itself.
Constants are factored out into installation-specific files known as
portbuild/conf/server.conf and portbuild/conf/client.conf. There is
only one server.conf file. Individual <arch> directories may have
their own client.conf files, or may symlink to ../conf/client.conf.
Note the removal of the hard-coding of INDEX.N, where N has to be
a single digit, and also have no '.' in it.
Feature safe: yes