Reconsider equality in XMLMap

[clange]

Comment moved from the source of XMLMap:

Is the current equality the kind of equality we want? Or should we instead consider the equality given by the pattern matching algorithm of ntn.rnd.Pattern? Comparing two XML elements is like pattern matching without placeholders -- we should either obtain an exception (unequal) or some non-null Matcher (equal). But note that we'd need to replace all placeholders by something "constant", e.g. om:OMVs with special names, as one cannot "match" a placeholder against a placeholder.
-- Christoph, 2008/01/25 (summarizing discussion with Normen)

[clange]

Citing a comment given by Dimitar:

I'm not sure if your comment in XMLMap is even possible to do, at least from performance point of view. That XMLMap is heavily used, and I even had to disable the XML diff there (the USE_XML_EQUALITY flag is false by default), because it was increasing the total running time for some 90%, and I'd rather allow a couple of duplicate entries than wait 10s for adding the simplest notation file. So I'm just guessing that doing sth like pattern matching there would make a lot more than 90%.