cmd/yacc: report correct line for 'default action causes potential type clash'
cmd/yacc: report correct line for 'default action causes potential type clash'

R=golang-dev, iant
CC=golang-dev
https://codereview.appspot.com/13588044

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