xml_dom.py: Added value_node(). Use new value_node() in value() and set_value(). set_value(): If the node already has a value node, reuse it instead of appending a new value node.

xpath.py: put_obj(): Return the id_attr_node using get_1() because it should only be one node

xml_func.py: _simplifyPath: Also treat the elem as empty if the required node exists but is empty

db_xml.py: put_table(): Added part of put() code that should be common to both functions

xpath.py: put_obj(): Return a tuple of the inserted node and the id attr node

xpath.py: set_id(): When creating the id_path, use obj() (which deepcopy()s the entire path) because it prevents pointers w/o targets

xpath.py: set_id(): When creating the id_path, deepcopy() the id_elem because its keys will change in the main copy

xpath.py: set_id(): Return the path to the ID attr, which can be used to change the ID

xpath.py: put_obj(): Return the inserted node so it can be used to change the inserted value

main Makefile: Maps validation: Fixed bug where there would be infinite recursion with the Maps validation section before the Subdir forwarding section (it's unknown why this is necessary)