[CMake] CPack error : Problem checking NSIS version with command: "C:/NSIS/makensis.exe" /VERSION

[Iosif Neitzke]

On both Windows 7 and Windows XP makensis.exe /VERSION seems to exit
normally, but it must be a bad return value or regex failure:

https://github.com/Kitware/CMake/blob/master/Source/CPack/cmCPackNSISGenerator.cxx#L437