modify Element.clone() for issue #763

[mct10]

Summary
I add a private instance Document.OutputSettings to record what output setting this element itself should follow. Also, I modify NodeUtils.outputSettings, which obtains the output setting of the node. It checks whether the node is element or not. If it is element, than check if it has an ownerDocument. If it does not have an ownerDocument, it will use the element's output setting. Or it will still follow the ownerDocument's output setting.

[mct10]

This is an attempt to solve #763

[jhy]

Thanks -- but I do not want to introduce another field to every Element in the DOM, as it really adds up how much memory is used in larger documents. Particularly for a (relative) edge case need as this.

My suggestion for a fix to the original issue would be to clone the parent Owner Document and attach that to the clone instead.