The mergemaster script is designed to aid you in updating the various
configuration and other files associated with OpenBSD.  The script
produces a temporary root environment using /usr/src/etc/Makefile which
builds the temporary directory structure from / down, then populates that
environment with the various files.  It then compares each file in that
environment to its installed counterpart.  When the script finds a change
in the new file, or there is no installed version of the new file it
gives you four options to deal with it.  You can install the new file as
is, delete the new file, merge the old and new files (as appropriate)
using sdiff(1) or leave the file in the temporary root environment to
merge by hand later.