fix backward-search in read-line
fix backward-search in read-line

Ignore-this: f62a012bbf026b1698dd368c228aea3b

darcs-hash:20100113135715-c41ad-c9b638fbaccee2349833cf24110012194d7e1d3b

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