The multi-argument CompressFiles(...) method has been replace by the
no-argument PackageFiles() method and 3 more member variables. This
will enable implemention of multi-package generators. Now each specific
generator (which overloads PackageFiles()) may decide to change the name
and/or the number of generated package files.
This allows for a built in bzip and zip capability, so external tools
will not be needed for these packagers. The cmake -E tar xf should be
able to handle all compression types now as well.