minor fix in Lwt.map
minor fix in Lwt.map

Ignore-this: 1ce184187e6afe31b8c2e3b99778cd7c

It was possible that [res] was connected two times, thus raising an
exception.

darcs-hash:20100528065410-c41ad-7882e8ad4ae46f0973efcc94e2cf6a49a877adcd.gz

avsm/lwt-OLD,avsm/lwt-OLD