[XML-SIG] copy node to new dom

[Martin v. Loewis]

>   I'd call minidom being "kind of" Level 2 (the namespace stuff) a bug
> in itself; it makes more sense to make it a Level 2 DOM.

Agreed. More precisely, DOM 2 Core; we don't do traversal, ranges,
HTML, events, etc (this still makes makes it "mini").

Regards,
Martin