Adding upstream version 1.2.3.

Signed-off-by: Daniel Baumann <daniel@debian.org>

selfupdate/log.go

@@ -0,0 +1,30 @@
+package selfupdate
+
+import (
+	"io/ioutil"
+	stdlog "log"
+	"os"
+)
+
+var log = stdlog.New(ioutil.Discard, "", 0)
+var logEnabled = false
+
+// EnableLog enables to output logging messages in library
+func EnableLog() {
+	if logEnabled {
+		return
+	}
+	logEnabled = true
+	log.SetOutput(os.Stderr)
+	log.SetFlags(stdlog.Ltime)
+}
+
+// DisableLog disables to output logging messages in library
+func DisableLog() {
+	if !logEnabled {
+		return
+	}
+	logEnabled = false
+	log.SetOutput(ioutil.Discard)
+	log.SetFlags(0)
+}