Undo Closed Tab: Add incognito="split"

I would like it if undo closed tab used separate storage for incognito and normal tab sessions, like the incognito="split" described here:

http://code.google.com/chrome/extensions/manifest.html#incognito

However, I think I tried building a custom extension in the past and there may be some more work needed than simply adding it to the manifest.

Thanks for the extension!
