runtime: fix SysFree to really free memory on Windows
runtime: fix SysFree to really free memory on Windows

Fixes issue 1294.

R=golang-dev, PeterGo, iant
CC=golang-dev
http://codereview.appspot.com/3271041

apparentlymart/golang,tv42/old-go,ssrl/go,tv42/old-go,gnanderson/go,apparentlymart/golang,pombredanne/go-deleteme,gnanderson/go,ssrl/go,tv42/old-go,h8liu/golang,apparentlymart/golang,pombredanne/go-deleteme,apparentlymart/golang,tv42/old-go,ssrl/go,h8liu/golang,dsriram/golang,gnanderson/go,dsriram/golang,ssrl/go,h8liu/golang,ssrl/go,gnanderson/go,dsriram/golang,apparentlymart/golang,h8liu/golang,gnanderson/go,pombredanne/go-deleteme,h8liu/golang,dsriram/golang,pombredanne/go-deleteme,dsriram/golang,ssrl/go,tv42/old-go,dsriram/golang,pombredanne/go-deleteme,ssrl/go,h8liu/golang,apparentlymart/golang,tv42/old-go,gnanderson/go,h8liu/golang,apparentlymart/golang,pombredanne/go-deleteme,tv42/old-go,gnanderson/go,pombredanne/go-deleteme,dsriram/golang