bug#25433: undo should restore cursor position too

[積丹尼 Dan Jacobson]

1. Accidentally paste (C-y) many many lines into the middle of the file
on the middle of your screen.

2. Your first reaction of course is to hit undo (C-/).

3. What you are looking at still leaves you worried. It sure doesn't
look like what you were looking at before the accident happened.

4. Your second reaction might be to hit undo again. Ahh, but that will
only make things worse!

Actually the first undo fixed everything back up. It just left the
cursor at a different position on the screen leaving you disoriented! It
shouldn't do that. Undo should restore cursor position too.

I bet that's how the undo found in browser menus works.

OK it might restore the cursor position, but does it restore the file
position in the whole window?