8547 update mandoc to 1.14.3

illumos/illumos-gate@c66b8046543352459a11a51501b628d1c98a8c44
https://github.com/illumos/illumos-gate/commit/c66b8046543352459a11a51501b628d1c98a8c44

https://www.illumos.org/issues/8547

update mandoc (now it's the official name) suite to new upstream version, which
among a lot of fixes, brings in much improved eqn(5)/tbl(5) support.

Reviewed by: Robert Mustacchi <rm@joyent.com>
Approved by: Richard Lowe <richlowe@richlowe.net>
Author: Yuri Pankov <yuri.pankov@nexenta.com>