python proxy checker ,change to threaded version

[Terry Reedy]

Rhodri James wrote:
> On Mon, 07 Dec 2009 18:21:23 -0000, Terry Reedy <tjreedy at udel.edu> wrote:

>>      def run(self):
>>        result = func(*func_args) # matching run_in_thread param names
>>        callback(result, *callback_args)
> Neat, but I think you mean
> 
>          if callback is not None:
>              callback(result, *callback_args)
> 
> for that last line.

yes [blush] I forgot to add 'untested ;-)