[nhc-bugs] "import qualified IO (readFile)" gives IO.readFile not defined

[Malcolm Wallace]

>     import qualified IO (readFile)
> 
>     Error when renaming::
>     Identifier IO.readFile used at 2:22 is not defined.

Indeed, at the moment readFile is not defined in the IO module.
It is actually a Prelude function.  However, according to the Report,
IO ought to re-export it (and all the other PreludeIO functions),
so I'll add a fix.

Regards,
    Malcolm