[go-nuts] data race testing code according "The Go Memory Model"

I read this article again http://golang.org/ref/mem
It read dry. Style like math article. Difficult to read at the beginning.
But the last line is IMPORTANT and easy to read.

Just use sync and channel instead of any OLD C style tips to prevent race
condition.

I've written some test code to try it.

go test -race -v -run I1 # detected
go test -race -v -run I2 # detected
go test -race -v -run I3 -timeout 3s # hang
go test -race -v -run I4 -timeout 3s # hang

The strange thing is: go routine hangs and the testing package's -timeout
option can not work.