fix(editor): a track bent by its second control vector is drawn bent: the straightening of a straight with control vectors (world/Track.cpp) checked the first vector twice, so with it left along the straight the second one, dragged with the gizmo, changed the data but not the track drawn; now a straight only where both vectors lie along it or aren't given. A track bent by hand into an S between two points dragged is labelled with its length (L 77 m), not with a radius of many kilometres read off it; the "K: split here" by the cursor isn't shown while a point is dragged; Ctrl+Z takes away the warning by the cursor of what it took back (the paths that left the kept design). The tutorial clips of editing recorded again: selecting and fixing without the gizmo (a joint dragged, the warning read, Ctrl+Z), and the new one of editing with the gizmo (Q, a control vector dragged bending the track, W, E)

application/editoruilayer.h

@@ -169,6 +169,8 @@ class editor_ui : public ui_layer
 	void set_status(std::string const &Status, bool const Error = false);
 	// a warning after an operation done: added to its status, shown by the cursor for a while
 	void set_notice(std::string const &Notice);
+	// the refusal or warning by the cursor taken away before its time, when what it tells of was taken back
+	void drop_refusal() { m_refusal.clear(); }
 
   private:
 	// methods