Keep original element styles as far as possible

Completely replacing the style on parent hidden elements means that where these have an explicitly set width and/or height then this will be removed and the calculated actual size may therefore be false.

Consider the following case:
```html
<!-- html, html, html -->
<style type="text/css">
.ohdear {width: 100%; height: 100%}
.invisible {width: 400px; height: 200px; position: relative; display: none;}
</style>
<!-- html, html, html -->
<div class="invisible" style="width: 200px; height: 100px">
<div class="ohdear"></div>
</div>
<!-- html, html, html -->
<script type="text/javascript">
// currently this will return 400; with this pull request it returns 200...
$(".ohdear").actual("width");
</script>
<!-- html, html, html -->
```