Element#clone should be changed to support decendent classes

[gwright]

Element#clone is current defined as

Element.new self

This has limited usefulness when self is actually a descendent of Element. The descendent class could of course also redefine clone but if Element#clone was defined as:

self.class.new self

Then the cloned object would automatically have the same class as self such that:

class MyElement < Element; end

e = Myelement.new 'foo'
other = e.clone
other.class        # -> MyElement (instead of Element)

would work as described.

BTW: Thanks for making REXML available!

[ser]

Implemented proposed fix.