Support auxiliary URIs in build client
Support auxiliary URIs in build client

This goes some way towards Issue #88, but unfortunately not all the way. See
the ticket for details.

grayjay/hackage-server,chrisdotcode/hackage-server,edsko/hackage-server,chrisdotcode/hackage-server,tkvogt/hackage-server,agrafix/hackage-server,dzackgarza/hackage-server,snoyberg/hackage-server,tkvogt/hackage-server,agrafix/hackage-server,grayjay/hackage-server,dzackgarza/hackage-server,edsko/hackage-server,erantapaa/hackage-server,haskell-infra/hackage-server,erantapaa/hackage-server,ocharles/hackage-server,ocharles/hackage-server,snoyberg/hackage-server