FAQ: variant types, unions Fixes issue 1935.
FAQ: variant types, unions
Fixes issue 1935.

R=rsc, bradfitz
CC=golang-dev
http://codereview.appspot.com/4850044

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang