[PATCH - revised] Thread::Queue 2.07

> The attached patch fixes Thread::Queue to handle the queuing of
>  structures with circular references.

Needed to put the new tests in a skip block conditionalized on the
threads::shared version.

• [PATCH] Thread::Queue 2.07 by Jerry D. Hedden
• [PATCH - revised] Thread::Queue 2.07 by Jerry D. Hedden
• Re: [PATCH - revised] Thread::Queue 2.07 by Rafael Garcia-Suarez