This is useful for places, like hashbang.sh, which have site-specific
modifications of the *.inc files.
With the current setup, the package manager cannot automatically install
updated versions of those files, as it would need to somehow merge the
site-specific and upstream changes. Having the site-specific changes in
separate files solves this.
This corresponds to commit ec719b9e0f4f7258b5f752af4857649a34a35dfe,
as submitted in netblue30/firejail#1034
This also overwrites our local firejail customizations, which are
re-added again in this branch.