Represent logged in time in seconds rather than minutes

This simplifies things.  In particular, it gets rid of random rounding
in getcommand(), which created a variation in the nightly build
depending on whether the update starts before or after the deity logs
out.

Replace struct natstr member nat_minused by nat_timeused, and update
cou_ca[] accordingly (this affects xdump nat).  Replace player member
minleft by timeleft, and getminleft() by gettimeleft().  Update
getcommand(), daychange(), player_main(), status() accordingly, taking
care not to change player output.  Change edit country key 'u' to work
in seconds.

src/lib/commands/play.c

@@ -101,8 +101,8 @@ play_list(struct player *joe)
        cname(joe->cnum),
        joe->cnum,
        player->god || joe->cnum == player->cnum ? praddr(joe) : "",
-       natp->nat_minused / 60,
-       natp->nat_minused % 60,
+       natp->nat_timeused / 3600,
+       (natp->nat_timeused % 3600) / 60,
        (long)(now - joe->curup));
 
     if (player->god) {