var tmpImg = new Image();

function change_image(old_img, new_img)
{

    tmpImg.src  = old_img.src;
    old_img.src = new_img.src;

}

function change_image_back(img)
{

    img.src = tmpImg.src; 

}

function clear_default_value(obj, default_value)
{

    if (obj.value == default_value) {
        obj.value = '';
    }

}

function change_style_class(obj, newClass)
{

    if (typeof obj.className != 'undefined') {
        obj.className = newClass;
    }

}

function l(url)
{

    window.location = url;

}

function is_pos_int(value)
{

    return (    !(Number(value) == NaN || Math.round(value) != value ||value < 1 )  );

}

function str_trim(str)
{

    return str.replace(/^\s+|\s+$/g,"");

}