Python 3.1.1 installer botches upgrade when installation is not on C drive.

[John Nagle]

    I just installed "python3.1.1.msi" on a system that had "python3.1.msi" 
installed in "D:/python31".  The installer found the old installation in
"D:/python31", partially trashed it, and then installed the new version
in "C:/python31".

    I uninstalled the failed install, and reinstalled.  On a new install,
the installer prompts for the destination dir, and that works.
Upgrade installs, though, are botched.

					John Nagle