Printing the number of msgs sent in test summary

The number of msgs sent during a performance test is now printed along
with the timing breakdown for each queue tested.
The PointerQ perf test sends unique pointers

Previously, we were sending the same pointer for every message. This
prevented us from checking for data races. Now we create a unique
pointer for each Write(...) and check that we are getting that pointer
on the corresponding Read(...). We do this by casting integers to
pointers using 'unsafe'.