go/parser: better error sync. if commas are missing
go/parser: better error sync. if commas are missing

R=rsc, bradfitz
CC=golang-dev
http://codereview.appspot.com/5756045

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