Installation of the Eigen source tree is currently done manually/recursively instead of by using the CMake feature INSTALL(DIRECTORY ...)
Is there a (historic) reason for that? It seems this is supported at least since CMake 2.6?
Good point, I don't see any reason to motivate the current state, except that the feature was probably missing when we started. So I'm OK to simplify that. This simplified solution is also more future proof.