Code review comment for lp:~vanvugt/mir/fix-1476201

I am willing to let test names go past 80 columns only sometimes. It would have to be a good name.

And yes I did describe the problem in detail particularly in test_buffer_queue.cpp. That same detail could be duplicated in buffer_queue.cpp but it's not a big concern how many times I fully comment the issue. In some ways the test suite is already more descriptive of use cases than the implementation.