Merge branch 'fix_reap_completion_race' into 'master'

emper/Runtime.cpp

emper/Runtime.hpp

emper/Scheduler.hpp

emper/io/GlobalIoContext.cpp

emper/io/IoContext.cpp

emper/io/IoContext.hpp

emper/io/Stats.hpp

emper/lib/adt/AtomicTryLock.hpp

emper/lib/sync/CountingTryLock.hpp