[CMake] Help to understand build process with rpath settings, for a pseudo destroot install on OSX (under macports)

[Darren Weber]

I need to understand how to use CMake command line variables to specify the
install name and rpath settings when building VTK and installing it into a
destroot (which is not the final installation path).  In macports,
everything is installed into a "holding bay" that is defined by $DESTROOT.