GHCi 6.0.1 on Mac OS X + emacs hangs; solution and patch

[Simon Marlow]

> The problem is caused by InteractiveUI.hs. It suppresses the 
> prompt when ghci's stdin is 
> not a tty (is_tty is false). Is there ever a reason to do 
> this? emacs needs the prompt to determine 
> when ghci's output has ended. If it never sees the prompt it 
> just waits forever. 

I think I did this so that you could run GHCi with the input piped in,
and not get any annoying prompts on the output:

  $ echo main | ghci -v0 Main.hs
  hello world!

Perhaps the prompt should be suppressed only when verbosity is zero
*and* the input is not a tty.  What do you think?

Cheers,
	Simon