title: InnoSetup: don't uninstall changed files
body: <p>How to tell InnoSetup to not uninstall (text) files which had been changed by the user (== are different from those installed by InnoSetup)?</p>
  
  <p>Or maybe more difficult: when installing a new version over an existing, InnoSetup should ask the user whether to overwrite the changed file, but on a pure uninstall, it should uninstall it without asking.</p>