avoid using absolute paths in generate CMake extra file

[dirk-thomas]

Instead of using the CMAKE_INSTALL_PREFIX in https://github.com/ros/cmake_modules/blob/master/cmake/cmake_modules-extras.cmake.develspace.in#L2 the Modules folder should be resolved relatively to ${cmake_modules_DIR} (e.g. like https://github.com/ros/gencpp/blob/hydro-devel/cmake/gencpp-extras.cmake.em).

[wjwwood]

You mean like this line?: https://github.com/ros/gencpp/blob/hydro-devel/cmake/gencpp-extras.cmake.em#L7

[dirk-thomas]

Yes, but you willl still need the conditional block to deal with the devel space.