enhancements to trees

Includes: 
_t_new_root (to create an empty root node), 
_t_add(to add an existing tree as a child to another tree), 
_t_node_index (to get the child index value of a node), 
_t_get_path (to get the full path of a given node) and 
_td (to dump out a tree for debugging)
semtrex groups now work