Allow directories in the source tree or build tree only if the
install tree is a subdirectory of the source tree or build tree,
as appropriate.
Re-use the test files in the RunCMake.include_directories test
to run in multiple scenarios. Bump the required CMake version
in the test to 3.0 to ensure that the new policy warnings are
emitted correctly.
Use preprocessor loops and add a unit test for the appropriate
policies. All policies whose value is recorded at target creation
time should be part of this list.
Stephen Kelly
Brad King