Avoid repeated hours and game down status notifications

Avoid repeated hours and game down status notifications

may_play_now() tells deities about hours restriction and game down
status.  It runs at login and before and after each command.  Getting
notified that often is annoying.

Avoid repetition by remembering notification in new player flags
PF_HOURS and PF_DOWN.  Add a notification when hours restriction has
been lifted.  Ensure the notification is printed before the prompt,
not before the command, by calling may_play_now() from command() only
for mortals.  Safe, because may_play_now() always returns true for
deities anyway.