Switch to the new man(1) command.

Switch to the new man(1) command.

* Exchange our old GNU man(1) command with the one from FreeBSD that I
  recently imported. It uses mandoc(1) by default. If mandoc(1) reports
  that it cannot render a page, man(1) will fall back to groff (right
  now our base groff, later the groff pkg when we remove it).

* Install mandoc(1) as apropos(1) and makewhatis(8). This means
  makewhatis moves from /usr/sbin to /usr/bin.

* Use mandoc(1) instead of groff for most purposes of bsd.man.mk.

* Remove /usr/share/man/cat*. It's not necessary anymore to cache
  formatted manual pages.