For things where we may have 2 major versions of the same software
installed in parallel (think of Qt and Python) make sure our version
selection gets this right.
If a variable exists called CMAKE_PROJECT_<projectName>_INCLUDE,
the file pointed to by that variable will be included as the last step
of the project command.
Some tests only need to run CMake to configure and generate a build
tree, but not actually perform the build. Add a new "Tests/CMakeOnly"
directory dedicated for this purpose. Add a helper script to drive each
test by creating a fresh build tree and running CMake on it. Add macro
"add_CMakeOnly_test" to help create tests using the script.
