add "IsWin64" variable, this variable is true if we are running on 64-bit Windows system even if it can be running in 32-bit mode
correct IsWin98 variable to be realy set only on Windows 98
add IsWin2000 variable for Windows version >= Windows 2000
enable define files for deletion together with installation files
add win64 host configuration to installer definition files to build installers with Win64 ost options