path/filepath: add test case for rooted ".."
path/filepath: add test case for rooted ".."

R=golang-dev, r
CC=golang-dev
http://codereview.appspot.com/6350047

Committer: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

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