[patch] setup.exe changes for Redownload/Reinstall Current version or Sources only - Part 2

[DJ Delorie]

I don't think setup needs to know the difference between a new install
and an upgrade, just some simple common-sense rules about the mount
table:

* Create the / mount.  This always happens, because we ask the user
  for it.

* For other mount points setup wants to create, check to see if the
  directory is non-empty.  If so, warn the user.  I'm not sure if
  setup can gracefully deal with a non-empty directory without a lot
  of extra logic.  I'm also not sure what to do with existing mounts
  that refer to subdirectories of the old root mount (if old root
  differs from new root).  It's probably a bad idea to keep them
  around, since you'd end up either mixing versions or corrupting the
  old installation, but should we delete them or map them into the new
  root?

* Now, read the *whole* mount table as it now stands.

* When creating files (either for its own purposes or while extracting
  a tar file), honor the mount table as-is.