mergesiteset automates upgrades of custom siteXY.tgz sets to a
different release of OpenBSD.

Modifications made to base system files are merged using merge(1).
Merge conflicts can be resolved in a text editor or with sdiff(1),
in a way similar to sysmerge(8).

Required OpenBSD installation sets will be downloaded and verified
automatically. Root privileges are not required. Regardless, file
permissions and ownership are preserved in the generated archive.
