* fhandler.cc (fhandler_base::close): Move setting isclosed() from here to

* fhandler.cc (fhandler_base::close): Move setting isclosed() from here to
closed().
(fhandler_base_overlapped::close): Correct comment.
(fhandler_base_overlapped::destroy_overlapped): Signal overlapped event before
closing it to potentially wake up a waiting thread.
(fhandler_base_overlapped::wait_overlapped): Expand setting of err when closed
to encompass non-signal event.  Test for a cancel event before making
nonblocking decisions.
* syscalls.cc (close): Set closed flag here so that any concurrently executing
functions will be notified ASAP.