Add support for non-NS and "prefix" shortcut confiscateAttr().
confiscateAttr() has two new forms, to ease usage. The first is with
two parameters, in which case a non-namespaced get and delete will be performed.
The second is that you do not have to pass the full namespace URI; if
you use a prefix that DOMFilter knows about, it will automatically substitute
it for you. By default, html and xml are known (however, you probably
won't need to use html).
Signed-off-by: Edward Z. Yang <edwardzyang@thewritingpot.com>