Missing Undo

[Rick Barrett]

It looks like undo isn't set up.

Steps to Reproduce:

Merge - Select ASE file

Options chosen: Create Shaders / Quick Storage

Ctrl-Z

Created materials are not removed

[Donovan Keith]

Resolved in b5c24bb. When opening and creating shaders, the multishader adds an undo step because CallButton is called, but I'm not convinced it's worth the effort to remove that.