Fourth or fifth try at this and finally found a way to make it work.
Absurd amount of busy-work forced on me by change in cabal's behavior.
Split up Utility modules that need posix stuff out of ones used by
Setup. Various other hacks around inability for Setup to use anything
that ifdefs a use of unix.
Probably lost a full day of my life to this.
This is how build systems make their users hate them. Just saying.
Since the user does not know whether it will run su or sudo, indicate
whether the password prompt will be for root or the user's password,
when possible.
I assume that programs like gksu that can prompt for either depending on
system setup will make clear in their prompt what they're asking for.
