Add a new build option, MAN_UTILS. This option lets you control building
utilities and related support files for manual pages, which were previously
controlled by MAN. For POLA, the default depends on MAN, i.e., WITHOUT_MAN
implies WITHOUT_MAN_UTILS and WITH_MAN implies WITH_MAN_UTILS.
Note this patch implicitly fixes a documentation bug of src.conf(5), which
says WITHOUT_MAN may be used to not build manual pages while it was also
disabling some utilities for manual pages.
Approved by: re (kib)