Fix for IE invalid argument for .html()

jQuery.html() throws an "invalid argument" error in IE if the string isn't completely valid html.

For example:
```
jQuery.html('My text with an <a href="#">anchor tag</a>.');
```
Doesn't work, while:
```
jQuery.html('<p>My text with an <a href="#">anchor tag</a>.</p>');
```
Does work.