cmd/api: show output of api tool even if exit status is 0
cmd/api: show output of api tool even if exit status is 0

We weren't seeing additions. (stuff to put in next.txt)

R=golang-dev, rsc
CC=golang-dev
https://codereview.appspot.com/12678043

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