MarkerManager getMarker methods should avoid creating temporary objects

// current
public static Marker getMarker(final String name) {
    MARKERS.putIfAbsent(name, new Log4jMarker(name));
    return MARKERS.get(name);
}

// proposed
public static Marker getMarker(final String name) {
    Marker result = MARKERS.get(name);
    if (result == null) {
        MARKERS.putIfAbsent(name, new Log4jMarker(name));
        result = MARKERS.get(name);
    }
    return result;
}