Pedigree editor's Undo function stops at the last import

I think i can do this for 1.4rcX, this may be a serious enough issue to fix? (e.g. you import, smth is broken, you try to undo, you can't - e.g. like during Brittney's demo last month. If anything, this is useful for us to have for 1.4-final for demos we do using 1.4).

That workflow is nothing like what a user would routinely do. Nobody imports on top of an existing pedigree. I'd like us to focus on problems that a high percentage of users may actually have instead of things that are so unlikely to happen.