Change man(1) to use mandoc to render manpages

man(1) now first test the manpage to run with mandoc to make sure it can be
rendered.
In case groff cannot be found (because base has been built WITHOUT_GROFF) it
recommands to install groff from the packages


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274901 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Fix typo


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274903 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
filedesc: plug a test for impossible condition in fgetvp_rights


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274904 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f