Represent logged in time in seconds rather than minutes

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.