[Pharo-project] Additional Test for Shared Queue (s)

While trying to track down a bug, I started thinking that there was a problem with SharedQueue. There isn't, but there were no tests that convinced me of that. So I wrote one that actually has two processes reading and writing many times to a Q. The same tests works for NSSharedQueue (except that the class under test is hard coded). I suggest that putting these tests in the appropriate packages/core would be a good idea. Tests attached.