patch applied (testsuite): Use extra_clean rather than clean

[Simon Marlow]

Ian Lynagh wrote:
> Sat Jun 28 08:27:43 PDT 2008  Ian Lynagh <igloo at earth.li>
>   * Use extra_clean rather than clean
>   This makes things more robust when running with threads
> 

Thanks, I'd been meaning to do that for a while.

Cheers,
	Simon