code: public boolean setChildAt(QuadTreeZone zone, N newChild) {
  		switch (zone) {
  		case NORTH_WEST:
  			return setFirstChild(newChild);
  		case NORTH_EAST:
  			return setSecondChild(newChild);
  		case SOUTH_WEST:
  			return setThirdChild(newChild);
  		case SOUTH_EAST:
  			return setFourthChild(newChild);
  		default:
  		}
  		return false;
  	}
docs: Set the child at the specified zone.
  
  @param zone is the zone to set
  @param newChild is the new node for the given zone
  @return <code>true</code> on success, <code>false</code> otherwise