Close the tempfile when journaling large messages

When we fail to log a message to journald due to ENOBUFS or EMSGSIZE, we
attempt to pass the message to journald by passing it a descriptor
attached to some shared memory.  We need to close the descriptor, too.

journal/journal.go

@@ -90,6 +90,7 @@ func Send(message string, priority Priority, vars map[string]string) error {
 		if err != nil {
 			return journalError(err.Error())
 		}
+		defer file.Close()
 		_, err = io.Copy(file, data)
 		if err != nil {
 			return journalError(err.Error())