selectAllChildren & extractContents do not extract all contents

[Ryosuke Niwa]

window.getSelection().selectAllChildren(test);
window.getSelection().getRangeAt(0).extractContents();

does not extract all the contents in test because we canonicalize the selection.

For example, if div was:
<div id="test"><a href="http://webkit.org/">hello</a></div>

The above script results in
<div id="test"><a href="http://webkit.org/"></a></div>

because the endContainer of getRangeAt(0) is "hello" (TextNode).