Modified k3m_in_range to move down the tree instead of up.
Modified k3m_in_range to move down the tree instead of up.

Moving up the tree is more efficient on averagewhen the search radius
changes because in this case the start point is most likely to be closest
to the query point.
When the radius is fixed however this advantage does not apply and
traveling down the tree is more efficient.

pschella/k3match,pschella/k3match