8l,6l: allow for more os threads to be created on Windows
8l,6l: allow for more os threads to be created on Windows

Program listed http://code.google.com/p/go/issues/detail?id=1495
(with nRequester set to 10000) will crash with

runtime: failed to create new OS thread (have 4526 already; errno=8)

instead of

runtime: failed to create new OS thread (have 618 already; errno=8).

R=golang-dev, rsc, vcc
CC=golang-dev
http://codereview.appspot.com/4172046

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang