Run timeouts that will expire in less than one millisecond.

The timeouts for poll and epoll are given in milliseconds,
which caused busy looping in the event loop for timeouts
with less time remaining.

evloop/timer.c

@@ -106,7 +106,7 @@ evtimers_run(void)
     evtimer_gettime(&now);
     while (timeheap_size() > 0) {
         struct timespec diff = subtime(timeheap_top(), now);
-        if (diff.tv_sec < 0) {
+        if (diff.tv_sec < 0 || (diff.tv_sec == 0 && diff.tv_nsec < 1000000)) {
             struct timeout *t = timeheap_remove_top();
             t->th.i = -1;
             t->cb(-1, EV_TIMEOUT, t->arg);