unix, windows: removed unused status parameter

async, timer, prepare, idle and check handles don't need the status parameter.

So, this closes issue #40.

I understand this will require many changes on dependant projects (mine included), but I'd go for it because it's just more correct. Also changes are pretty simple :-)

Now, since we seem to be pretty close to v0.12, we could merge this after, I'd also be ok with that.

/cc @indutny, @piscisaureus, @bnoordhuis