Aimee OS variants can now supply a `semange.mods` file in their
configuration directories. This file contains SELinux customizations,
in the format produced by `semanage export`. Variants can use this
mechanism to set SELinux booleans, change user/login mappings, and other
SELinux policy customization. At build time, the base `selinux.mods`
file in the source directory is combined with the variant's file, if it
exists, and the resultant customizations are applied in a single
transaction.