lib/codereview: Unable to use vim for 'hg change' from windows console
reload(sys) break workaround for windows.
see:
http://mercurial.selenic.com/bts/issue2888
http://mercurial.selenic.com/bts/issue1452
Also does not work with backslash paths.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5150054