TSAN caught subtle error when exiting transport_test (exercise mode); worker loop should be stopped before things that tasks posted-onto it touch get destroyed in dtor. So doing that now. Assuming I got that right transport_test will finish fine with TSAN, in exercise mode, at least in heap sub-mode (SHM-classic and SHM-jemalloc sub-modes TBD). Also updating submodules (comment/spacing only changes). #38