ui/list: do not use data-joshfire-child

[dieppe]

line 434:

var lastOffset = itemContainer.children().last().data('joshfire-child');

should be replaced (why not use this.items.length ?)

line 578:

var el = container.find('> ' + tagName + '[data-joshfire-child=' + offset + ']')[0];

should read something like

var el = container.find('> ' + tagName + ':eq(' + offset + ')')[0];