cet-is

Based on information in the CMake documentation for configure_package_config_file (see the description of the INSTALL_PREFIX option), it would appear that it is feasible (and reasonable) to create a second -config.cmake file (e.g. at include(CetCMakeEnv) time) configured to do the right thing at build-time.

In combination with teaching MRB to construct its top-level CMakeLists.txt file to add_subdirectory in the right order, this should drastically simplify the special code required to configure a package for inclusion in a multi-package build, and render it consistent with the code required to do the same thing both for a single-package, non-MRB build and utilizing a pre-built external product (find_ups_package in all cases). It should also remove the need for explicit manipulation of the CMAKE_MODULE_PATH in all package-level CMakeLists.txt files.