title: How to I make CPack (NSIS) upgrade properly for new installations?
body: <p>I'm using the CPack NSIS generator to create an installer. However, each time I release a new version, our users are running the new installer without uninstalling the old version (which is understandable).</p>
  
  <p>Is it possible to make the installer overwrite all existing files? Failing that, is there a way to block the installation if it's already installed?</p>
  
  <p>Also, our CPack call is wrapped in another script, as a last resort, is it possible for me to hack/reconfigure the project.nsi file so that it does one of the above?</p>