XAddHosts fails if any of the entries in the list fails.
The gdm-initial-setup user isn't available on most systems,
so XAddHosts fails on most systems.

Upshot is, since commit 189cd818bf1592b5b8607793575bcf4e71ba8008
most people have been relying on xauth cookies for X authorization.
xauth cookies aren't nearly as robust across hostname changes, so
that's not ideal.

This commit calls XAddHost() 3 times instead of one XAddHosts
call to work around the problem.  Ideally, we'd only add
gdm-initial-setup when we need it instead of all the time.

That will have to come later.