goinstall: check for error from exec.*Cmd.Wait() before using its result
goinstall: check for error from exec.*Cmd.Wait() before using its result

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/1923043

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

tav/go,tav/go,tav/go,tav/go,tav/go,tav/go,tav/go