Fix testAppendToPrependTo and testInsertBeforeInsertAfter for IE.

On IE only emptying out the parent element of an inserted element
for which a reference still exists causes the element to be emptied
out as well:

```
var element = $('<div>hello!</div>')
element.appendTo('body')
$('body').html('')

element.get(0).innerHTML
// => '' on IE
// => 'hello!' on other browsers
```

Thie behavior is expected and matches jQuery.