gotest still assumes that gopack is in your PATH

If your $PATH does not include $GOBIN then
the build fails at the first *.a file, which
is probably when running the tests for tar

R=rsc
CC=golang-dev
https://golang.org/cl/193066

src/cmd/gotest/gotest

@@ -119,7 +119,7 @@ nmgrep() {
 		# Figure out pkg.
 		case "$i" in
 		*.a)
-			pkg=$(gopack p $i __.PKGDEF | sed -n 's/^package //p' | sed 1q)
+			pkg=$("$GOBIN"/gopack p $i __.PKGDEF | sed -n 's/^package //p' | sed 1q)
 			;;
 		*)
 			pkg=$(sed -n 's/^ .* in package "\(.*\)".*/\1/p' $i | sed 1q)