compiler: Better error messages for { on line after if/for/switch.
compiler: Better error messages for { on line after if/for/switch.

R=iant
CC=gofrontend-dev
https://golang.org/cl/41520043

qskycolor/gofrontend,anlhord/gofrontend,anlhord/gofrontend,anlhord/gofrontend,golang/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,golang/gofrontend,golang/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,golang/gofrontend,anlhord/gofrontend