Improve getPointedThing() (#4346)

* Improved getPointedThing()

The new algorithm checks every node exactly once.
Now the point and normal vector of the collision is also returned in the
PointedThing (currently they are not used outside of the function).
Now the CNodeDefManager keeps the union of all possible nodeboxes, so
the raycast won't miss any nodes. Also if there are only small
nodeboxes, getPointedThing() is exceptionally fast.
Also adds unit test for VoxelLineIterator.

* Cleanup, code move

This commit moves getPointedThing() and
Client::getSelectedActiveObject() to ClientEnvironment.
The map nodes now can decide which neighbors they are connecting to
(MapNode::getNeighbors()).

src/map.h

@@ -193,6 +193,8 @@ public:
 	virtual MapBlock * emergeBlock(v3s16 p, bool create_blank=true)
 	{ return getBlockNoCreateNoEx(p); }
 
+	inline INodeDefManager * getNodeDefManager() { return m_nodedef; }
+
 	// Returns InvalidPositionException if not found
 	bool isNodeUnderground(v3s16 p);
 
@@ -346,6 +348,9 @@ protected:
 	// Queued transforming water nodes
 	UniqueQueue<v3s16> m_transforming_liquid;
 
+	// This stores the properties of the nodes on the map.
+	INodeDefManager *m_nodedef;
+
 private:
 	f32 m_transforming_liquid_loop_count_multiplier;
 	u32 m_unprocessed_count;