fix windows build: always use / in filenames of go/doc test output
fix windows build: always use / in filenames of go/doc test output

R=r
CC=golang-dev
http://codereview.appspot.com/5554055
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go