Code review comment for lp:~jelmer/launchpad/bug471148

This makes it possible for processor families to be marked restricted. Source packages in archives will only be built using these processor families if they are explicitly permitted, using an entry in ArchiveArch.

This patch also adds some infrastructure to create processor families and processors, which we use for testing.

I reran "make newsampledata" which doesn't appear to have happened in a while, so there are some updates there related to earlier branches as well.