test: add test for issue 4468 (go/defer expr may not be parenthesized)
test: add test for issue 4468 (go/defer expr may not be parenthesized)

R=gri
CC=golang-dev
https://codereview.appspot.com/6870053

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