Chris Davis points out that GetQueuedCompletionStatus
sometimes returns false not to report "No events for
you!" but instead to report "An overlapped operation
failed." Add a way to tell an event_overlapped that
its operation failed.
svn:r1490
This is stuff that it's easy to get wrong (as I noticed when writing
bench_http), and that takes up a fair amount of space (see http.c).
Also, it's something that we'll eventually want to abstract to use
IOCP, where available.
svn:r1272