#4 package-archives should permit failovers

[Heather Sherman]

Currently the syntax of etc/package-archives is one line
per _required_ package archive. If any archive is
unavailable
a build will fail.

I suggest we provide for replication by changing the
file syntax to permit users to list failover package
archives on the same line. For example:

http://packagearchive.mycompany.com
http://wigwam-framework.org http://backup-framework.org

would mean that "packagearchive.mycompany.com" must be
available and that either of the package archives on
the second line must be available.

Heather