Move threads test added in change 32091

This patch moves the test added by change 32091 from
ext/threads/t/problems.t to t/op/threads.t.  The rationale
is that the code change is in core and not the threads
module code.

On 10/10/2007, Jerry D. Hedden <jdheddencpan.org> wrote:
> This patch moves the test added by change 32091 from
> ext/threads/t/problems.t to t/op/threads.t.  The
rationale
> is that the code change is in core and not the threads
> module code.

Thanks, applied.