Replace use of attr with prop for booleans
    
    Recommened way of setting boolean HTML attributes is by $.prop(boolean) method not $.attr(boolean) because it sets DOM object property not an attribute. Latter works because of jquery's backward compatibility. This patch makes things clearer.
    
    Some info about prop and attr: http://stackoverflow.com/a/5876747
    
    https://fedorahosted.org/freeipa/ticket/2817