test: add bug439, valid code that caused a gccgo crash
test: add bug439, valid code that caused a gccgo crash

R=golang-dev, bradfitz
CC=golang-dev
http://codereview.appspot.com/6198075
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go