Previously, these library locations were set absolutely. This
prevented overriding their locations with environment variables. Now,
setting the corresponding environment variable will override the
setting in the environment wrapper. For instance, I can set
KISYSMOD=/some/path/to/footprints
and this will be used as my footprint library instead of the default
footprint library in the nix store. This feature is particularly
useful for having kicad libraries which are writable.
9320c69ecb