8050044: (process) Increase reaper thread native stack size by a factor of 2

[Rob McKenna]

Hi folks,

A very simple change suggested by Martin a while back in another review. 
I'm just getting around to it now:

bug: https://bugs.openjdk.java.net/browse/JDK-8050044
webrev: http://cr.openjdk.java.net/~robm/8050044/webrev.01/

Martins comments: 
http://mail.openjdk.java.net/pipermail/core-libs-dev/2014-March/025943.html

     -Rob