Consistent const string params

Parent commit broke behaviour.
Thanks @TeTpaAka for testing the fix.

src/serverobject.h

@@ -151,9 +151,9 @@ class ServerActiveObject : public ActiveObject
 	{}
 	virtual void setAnimation(v2f frames, float frame_speed, float frame_blend)
 	{}
-	virtual void setBonePosition(std::string bone, v3f position, v3f rotation)
+	virtual void setBonePosition(const std::string &bone, v3f position, v3f rotation)
 	{}
-	virtual void setAttachment(int parent_id, std::string bone, v3f position, v3f rotation)
+	virtual void setAttachment(int parent_id, const std::string &bone, v3f position, v3f rotation)
 	{}
 	virtual ObjectProperties* accessObjectProperties()
 	{ return NULL; }