go/parser: expressions may have comments
go/parser: expressions may have comments

Thanks to 0xE2.0x9A.0x9B for the patch suggestion.

Fixes issue 2739.

R=r
CC=golang-dev
http://codereview.appspot.com/5536071

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