* errno.cc (errmap): Add mapping for ERROR_IO_INCOMPLETE.

* errno.cc (errmap): Add mapping for ERROR_IO_INCOMPLETE.
* fhandler.cc (fhandler_base::fcntl): Fix comment.
(fhandler_base::wait_overlapped): Accept an optional len parameter.  Use the
len parameter when WriteFile fails with ERROR_IO_PENDING.  Make debug output
less alarming.
(fhandler_base::write_overlapped): Pass len to wait_overlapped.
* fhandler.h (fhandler_base::wait_overlapped): Add an optional argument
denoting the number of characters intended to be written.
* fhandler_tty.cc (fhandler_pty_master::close): Don't close archetype handles
when cygwin is still initializing since the handles aren't actually opened at
that point.