Another typo in Thread.pmod on 7.8

[Jeff Hungerford]

It looks like this is fixed in 8.0, but in 7.8
Thread.Farm()->run() doesn't connect the returned result
object to the job in the queue.

Line 661 is:
 job_queue->write( ({ 0, ({f, args }) }) );

But it should be:
 job_queue->write( ({ ro, ({f, args }) }) );

-Jeff