RFR (S): 8155810: Bound the number of root region scan threads to the number of survivor regions

[Thomas Schatzl]

Hi Jon,

On Wed, 2016-05-11 at 07:50 -0700, Jon Masamitsu wrote:
> Looks good.
> 

  thanks for the re-review. As you might have noticed, I already pushed
this after Stefan's go-ahead to meet FC cutoff date. Sorry.

Thanks,
  Thomas