Roll gofrontend to ca381cdd378c

This updates us to Go 1.3 release. This isn't ready to go in yet, but
I wanted to publish it now to avoid duplicated work. Known issues:

1) The following CLs need to land in gofrontend:
   https://codereview.appspot.com/110710043/
   https://codereview.appspot.com/115870044/
   https://codereview.appspot.com/117990043/

2) There is an issue when using Clang which causes frequent panics with
   the message "fatal error: bad g status". This can be worked around by
   setting LIBGO_CC=gcc but I would prefer to try to fix this issue before
   landing this.