shutdown: Assume absolute time is in the future

The original bug describes it best:

When an absolute time is specified to shutdown, the program's
behavior depends on whether that time has passed during the
current calendar day. POLA would suggest that for shutdown,
whose time argument is always supposed to be in the future,
absolute times specified without a specific date should refer
to the next occurrence of that time, rather than erroring out
if that time has already passed during the current day.

PR: 32411
Submitted by: wollman@khavrinen.lcs.mit.edu
Submitted on: 2001-11-30 20:30:01 UTC
Reviewed by: asmodai (at time of bug submission)