[platform-ui-dev] Undo goes past the last commit in AbstractTextEditor

["Randy Hudson" <hudsonr@xxxxxxxxxx>]

Why am I able to undo past the last commit (Save)?  Sometimes I
accidentally type a key because I am trying to use an accelerator, and I
dirty the Editor.  I would think that I should be able to hit undo and see
what I did that *Isn't* saved.  But I can't, because undo keeps going past
that erroneous character, into things that I know I have already committed.

I find this confusing.  In fact, it's strange that doing a save removes the
Dirty flag, because if I close and reopen the text file I lose information:
the stuff that used to be undoable because it wasn't flushed.

GEF actually uses the undo stack to determine "dirty"-ness.  And, if the
user un-does overthing, the Editor is no longer dirty.