- Avoid that mandb-symlink-target-timestamp fools us

- Workaround missing groff-full to get refer(1), the bibliographic
preprocessor found

- Update to man-db 2.10.0 (4 February 2022)
* Manpath deduplication no longer mishandles the case where another entry
in the manpath is a suffix of a candidate path to append.
* Fix potential crash in path searching if `getcwd` fails for reasons other
than running out of memory.
* Fix crash in `globbing` test tool if run with no non-option arguments.
* `lexgrog` now produces output in the user's locale.
* Downgrade "malformed .lf request" warning to a debug message and rephrase
it somewhat, since `.lf` requests can use `*roff` arithmetic expressions
and we can't reasonably parse those.
* Avoid modifying the database without changing its mtime, which had been
possible since 2.7.0 if `mandb`'s purge phase found work to do but the
main phase didn't, and which confused some backup systems into reporting
possible filesystem corruption.
* `man` no longer inadvertently modifies the `MANSECT` environment variable
before passing it on to its subprocesses.
* `mandb` now stores the mtime of link targets as the mtime of their
corresponding database entries, rather than sometimes storing the mtime
of the link instead.
* Since man-db 2.4.2, `man` has behaved as if the `-l` option was given if
a manual page argument contains a slash. Since man-db 2.5.6, this has
interacted slightly poorly with the subpage feature, emitting spurious
error messages if given multiple manual page arguments some of which
include a slash. `man` no longer emits spurious error messages in this
case.