Implements the
Comparator interface for DOM namespace attributes. An attribute
is a namespace attribute either if its prefix equals "xmlns", or if its qualified name equals "xmlns".
The namespace prefix of the namespace attribute is used as the primary key for the comparison. If a
prefix is not defined (default namespace declaration), the attribute is lexicographically least, i.e.
an attribute with a qualified name "xmlns" is less than an attribute with qualified name
"xmlns:anyPrefix". If the primary key of the attributes are equal, the local name of the
attributes acts as the secondary key.
PLEASE NOTE: The ordering imposed by this
Comparator implementation is NOT consistent
with equals!