Windows fixes

- Fix XP support: get pointer to CancelIoEx at runtime.
- Fix overlapped IO.
- Don't use overlapped IO if direct or synchronous options are set.
- Check if write option is set before opening file in read-only mode:
  fixes 'rw=rw'.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
3 files changed