bump go1.4rc1 tag
bump go1.4rc1 tag

Now that the build and builders are fixed, we're good to go.

LGTM=dsymonds
R=rsc, dsymonds
CC=golang-codereviews
https://codereview.appspot.com/177900043

firebitsbr/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,wesolows/golang-old,wesolows/golang-old,wesolows/golang,wesolows/golang,wesolows/golang