goinstall: let git/hg/svn create the final directory element
goinstall: let git/hg/svn create the final directory element

R=r
CC=golang-dev
http://codereview.appspot.com/634044
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go