Replace daychange() and gettimeleft() by update_timeused_login(),
update_timeused() and enforce_minimum_session_time(). The new
code doesn't assume the day is always 24 hours long which can
occur when transitioning into or out of DST and such. Logging
in after more a multiple of 128 days now resets nat_timeused
properly.
Fix nat_timeused calculation on midnight rollover to include
the time since midnight.
struct natstr member nat_dayno and struct player member timeleft
are now unused, remove them.
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.
