Use the xml property instead in IE for serializing XML.
The xml_eql tests were failing in IE9 on a difference between null and an
empty string for namespaceURI of attributes, this difference is not
relevant to our testing so make sure we ignore.
This also involves some modifications to the xmleql functionality now that
it was tested with a real-life case (KML). Also, some of the input KML files
needed to be changed since we currently cannot roundtrip 100% of the input.
This adds some improvements for the xmleql test assertion. When passed in a
document, use the documentElement. Also improve error reporting as suggested
by @tschaub.
