ghci and ghc -threaded broken with pipes & forking

[Malcolm Wallace]

> > Had you deprecated the non-threaded RTS, we would probably have no
> > problems described in ticket #2848 :-/
> 
> > I think you'll have to deprecate it anyway, because it will be more
> > and more difficult to maintain two versions of code,
> 
> we may conduct small survey on amount of usage of old RTS (i mean ask
> this in haskell-cafe)

For the only application I tried, using the threaded RTS imposes a 100%
performance penalty - i.e. computation time doubles, compared to the
non-threaded RTS.  This was with ghc-6.8.2, and maybe the overhead has
improved since then?

Regards,
    Malcolm