call Lwt.wakeup_paused before polling the thread in Lwt_main.run

Ignore-this: 5f06d56e6d89d9b984f3ce41659beaa3

Otherwise, if the thread terminates in wakeup_paused, the scheduler
may wait indefinitly for nothing.

darcs-hash:20100504133633-c41ad-7976869aa57bc45fe37045a1dc9cd46defcf5ec9

src/unix/lwt_main.ml

@@ -72,6 +72,7 @@ let default_iteration () =
 let main_loop_iteration = ref default_iteration
 
 let rec run t =
+  Lwt.wakeup_paused ();
   match Lwt.poll t with
     | Some x ->
         x