Allow non-slides in the .slide-group.

[kitsunde]

The way the slider works right now is that it counts the children of the .slide-group even if those children are not .slide this include elements without size like <script>. This is incompatible with emberjs that injects script tags into the DOM to keep track of data binding. So if you do something like this:

<div class="slider">
    <div class="slide-group">
        {{#each}}
            <div class="slide">{{this}}</div>
        {{/each}}
    </div>
</div>

The DOM will look something like:

<div class="slider">
    <div class="slide-group">
        <script id="metamorph-11-start" type="text/x-placeholder"></script><script id="metamorph-14-start" type="text/x-placeholder"></script>
        <div class="slide">foo</div>
        <script id="metamorph-14-end" type="text/x-placeholder"></script><script id="metamorph-11-end" type="text/x-placeholder"></script>
    </div>
</div>

And the slider will think there's 3 slides.