I'm installing on a slow computer. After some questions it takes
considerable time for the next screen to show up. My request is that
immediately after a question is answered, before doing heavy
processing, the screen is cleared.

This will prevent oopses like the just occured to me:
* Re-entered my user password for confirmation
* Did something off-computer for a few seconds
* Came back, saw the "re-enter your password" dialog still up, thought
  "oh, forgot that I have to enter it two times", stuffed the password
  and return into the keyboard buffer.
* A second later the next question (about ppp) popped up and was
  answered wrongly by my return. (Thankfully my password did not end
  up in a textbox ...)

A way to back up to the last question is fine too to fix this. That
would be more generally useful, but perhaps harder to implement.

TIA