Switch to mandoc's version of makewhatis(8), whatis(1), apropos(1) utilities.

This change among other things improve search capabilities over the manpages
allowing fine grain query.

A new build option WITHOUT_MANDOCDB has been added to keep the ancient version
of the database and the tools. The plan is to entirely remove this option before
11.0-RELEASE.

Differential Revision: https://reviews.freebsd.org/D2603