Work around suspected broken logic in the handling
of TESTSBASE and/or TESTSDIR in base/head/.

My observations suggest when TESTSBASE is specified
as a make(1) variable, DESTDIR seems to get lost if
NO_ROOT is also specified.

To work around this, export DESTDIR earlier, and
explicitly prefix TESTSBASE and TESTSDIR with its
value.

This fixed refreshing the man-refs.ent file from
a recent checkout of base/head/.

While here, bump the Copyright year.

Sponsored by: The FreeBSD Foundation