add hacks for windows in Lwt_unix
add hacks for windows in Lwt_unix

Ignore-this: 48811fcae1e97a8156e69d43f9f8df22

darcs-hash:20100401000442-c41ad-25399f24c752ce4a3e92965d34838b84fcfbfef5

rgrinberg/lwt,gfxmonk/lwt,mfp/lwt,gfxmonk/lwt,fdopen/lwt,ocsigen/lwt,ocsigen/lwt,rgrinberg/lwt,janestreet/lwt-async,c-cube/lwt,rneswold/lwt,mirage/lwt,ocsigen/lwt,c-cube/lwt,rneswold/lwt,rgrinberg/lwt,mirage/lwt,rneswold/lwt,c-cube/lwt,janestreet/lwt-async,fdopen/lwt,rgrinberg/lwt,mfp/lwt