go/build: fix TestBogusDirectory format and maybe Windows failure
go/build: fix TestBogusDirectory format and maybe Windows failure

R=golang-dev, adg
CC=golang-dev
https://codereview.appspot.com/7183046

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