Fix handling of trailing punctuation in .Lk.

Fix handling of trailing punctuation in .Lk.
This macro is unusual in so far as trailing punction needs to remain
inside the scope because it must be inside, not after the display
of long URIs in terminal output mode.
Improves formatting of fw_update(1), help(1), less(1), sendbug(1),
acx(4), inet6(4), ipsec(4), oce(4), isakmpd.conf(5), afterboot(8),
release(8), traceroute(8).