add type annotations in Lwt_io for ocaml 3.13
add type annotations in Lwt_io for ocaml 3.13

Ignore-this: 8ed4603836cdec5eff44e9658ffc5ebc

darcs-hash:20110815204408-c41ad-e084d5fc6660b2ec571da7ae5ab04d5eba07549d.gz

avsm/lwt-OLD,avsm/lwt-OLD