Re-prepare statement throttle

[Bouncheck]

I still need to further test this, but code is more or less how I want to do this.

[dkropachev]

@Bouncheck , let's review it, it looks good, only my concern is that RequestHandler.onSet is run for different connections and requests and if between these requests RequestHandler keeps state you are going to have problem with accumulating errors are reaching limit, which is going to make this instance of RequestHandler unoperational.