of what the documentation claimed) with a new one that is parsed and
callable, and far simplyer -- it turns ".Nx FOO ." into "NetBSD FOO."
without needing to have version numbers hard coded in.
Add a .Fx macro that is a copy of the .Nx macro except that it prints
"FreeBSD" instead of "NetBSD" -- this should make any future "HISTORY"
sections which credit FreeBSD easier, and will not require that we
constantly track their macro versions.
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