The remaining items in #3427 were non-issues, see comment in #3427. Instead, this patch is adding two tests. Both are derivatives of api.detach_spawn.
api.detach_spawn_quick_exit: Adds start/stop_and_cleanup re-attach to api.detach_spawn. It only spawns one thread. The thread is synch'd such that it exits while running native. This case is not supported by DynamoRIO's dr_app_stop w/o detach, but must work w/ dr_app_stop_and_cleanup().
api.detach_spawn_stress: Adds start/stop_and_cleanup re-attach to api.detach_spawn. Increase the number of spawned parent and child threads to 25 each, spawning a total number of 25 + 25 * 25 = 650 threads at a time, but limit the re-spawn loop. Like api.detach_spawn, this test is currently flaky in 32-bit, and very rarely flaky in 64-bit. #3427 covers the 64-bit failure. I have added a comment to #2694.