* fhandler.cc (fhandler_base_overlapped::wait_overlapped): Remove special

* fhandler.cc (fhandler_base_overlapped::wait_overlapped): Remove special
treatment for ERROR_NO_SYSTEM_RESOURCES.  Cancel I/O and reset the overlapped
handle on error.
(fhandler_base_overlapped::write_overlapped): Limit writes to max_atomic_write
bytes in blocking case.  Incorporate code from now-defunct
write_overlapped_fallback.  Fix serious oversight where ptr was not advanced as
buffer was written.
(fhandler_base_overlapped::write_overlapped_fallback): Eliminate.
* fhandler.h (fhandler_base_overlapped::write_overlapped_fallback): Ditto for
declaration.
(DEFAULT_PIPEBUFSIZE): Lower size to slightly less than documented worst-case
atomic write size.
(fhandler_overlapped::wait_return): Remove unused element.