os: make RemoveAll() work on windows
os: make RemoveAll() work on windows

R=golang-dev, rsc1
CC=golang-dev
http://codereview.appspot.com/2212041

Committer: Alex Brainman <54ba58c8441b5eff861de6b4e5ee46baf086b142@gmail.com>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go