Find a node in the tree
@param x node value to find (in) @param cnt number of nodes smaller than or equal to _x_; can be NULL (out)
@return node equal to _x_ if present, or NULL if absent
See Implementation
Find a node in the tree
@param x node value to find (in) @param cnt number of nodes smaller than or equal to _x_; can be NULL (out)
@return node equal to _x_ if present, or NULL if absent