/* 
** (for now) imageUri must be site-relative
*/
function imagePopup (imageUri, title, height, width) {
    var uri='/image-popup?title=' + title + '&uri=' + imageUri;
    var properties = "";    // whatever
    properties += height ? (' height=' + height + ',') : null;
    properties += width ? (' width=' + width + ',') : null;
    properties += 'toolbar=0, status=0, menubar=0';
    self.open (uri, '_blank', properties);
}