sleepAsync sleeps for too long

[yglukhov]

Tested on macos:

import asyncdispatch
import times

proc main() {.async.} =
    echo "1: ", epochTime()
    await sleepAsync(1) # wait for 1 ms. Actual result (see below): ~500 ms
    echo "2: ", epochTime()
    await sleepAsync(1) # wait for 1 ms.  Actual result (see below): ~500 ms
    echo "3: ", epochTime()

asyncCheck main()

runForever()

nim c -r ~/test.nim

1: 1461774804.308667
2: 1461774804.81404
3: 1461774805.315593

[ghost]

That's because the default polling timeout is set to 500 ms, right? is it an unintended consequence?