doc/go1.3.html: Plan 9 support
doc/go1.3.html: Plan 9 support

LGTM=aram, r
R=r, aram, bradfitz
CC=golang-codereviews, rsc
https://codereview.appspot.com/89130045

apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang