Hily Jiang

Fix concurrent data race problem

3

Data race test failed when in concurrent systems. The test code can be found here: #74

``` go package main import ( "os" "time" "github.com/op/go-logging" ) func main() { go func() { test("test1") }() test("test2") time.Sleep(time.Second) } func test(name string) { backend := logging.NewLogBackend(os.Stdout, "", 0)...