libeio bugfix part 2

Reverts the change to deps/libeio/eio.c added in
04dd2d51be
It wasn't a bug, I was just using eio incorrectly.

See http://lists.schmorp.de/pipermail/libev/2010q1/000855.html

deps/libeio/eio.c

@@ -548,9 +548,6 @@ static int etp_poll (void)
         }
     }
 
-  if (want_poll_cb)
-    want_poll_cb ();
-
   errno = EAGAIN;
   return -1;
 }

src/node.cc

@@ -721,7 +721,9 @@ static void EIOCallback(EV_P_ ev_async *watcher, int revents) {
   assert(revents == EV_ASYNC);
   // Give control to EIO to process responses. In nearly every case
   // EIOPromise::After() (file.cc) is called once EIO receives the response.
-  eio_poll();
+  if (-1 == eio_poll() && !ev_async_pending(&eio_watcher)) {
+    ev_async_send(EV_DEFAULT_UC_ &eio_watcher);
+  }
 }
 
 // EIOWantPoll() is called from the EIO thread pool each time an EIO