ipc::transport::struc::Channel API now formally allows concurrent calls of its APIs on the same object including .sync_request(). .sync_request()s will execute fully serially, even if a blocking-wait is necessary; but any other call during a .sync_request() blocking-wait shall execute immediately. / ipc::session::shm::arena_lend::jemalloc::Shm_session internal improvement (no effect on functionality).#141