WiX: detect old WDS installation

[avogelba]

Originally reported by: Oliver (Bitbucket: assarbad, GitHub: assarbad)

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• Windows 7, 64bit
  • HKEY_CURRENT_USER\Software\Seifert\WinDirStat
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Uninstall\WinDirStat
  • C:\Program Files (x86)\WinDirStat (Uninstall.exe)
• Windows XP, 32bit
  • HKEY_CURRENT_USER\Software\Seifert\WinDirStat
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Uninstall\WinDirStat
  • C:\Program Files\WinDirStat (Uninstall.exe)

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• Bitbucket: https://bitbucket.org/windirstat/windirstat/issue/96