Change Type in Scene Tree Doesn't Mark The Scene as Modified

[nazgulsenpai]

Godot version:
Master eaa5dfb

OS/device including version:
Windows 10 64bit, OSX

Issue description:
Using the Change Type item in the Context Menu of the Scene Tree does not trigger that the scene has been modified.

Steps to reproduce:
Select any node in a scene that's unmodified and Change Type. Notice the asterisk in the Scene name indicating a change since saving is not present.

[reduz]

Because it clears the undo/redo, but its a good point