tag go1.4rc1

LGTM=dsymonds
R=rsc, dsymonds
CC=golang-codereviews
https://codereview.appspot.com/175840043
misc/makerelease: use release-branch.go1.4 for tools and tour

TBR=rsc
R=rsc
CC=golang-codereviews
https://codereview.appspot.com/175870043