Balancer should not reassign (because of overloading) a region that was just opened

I'm running a mapreduce job. I see a region split and its daughters come on line and then 8 seconds later, master judges the regionserver overloaded and so closes the just-opened region. This messes up clients. They may have just picked up the new location for their row query and now its moved again and client has to go hunting anew.

We need to assign the vintage regions first.

I'm going to change balancer slop. Its not sloppy enough and balancing cuts in too early.