Include "inttostr.h".

Include "inttostr.h".
(human_time): Print the date/time as a number of seconds since the
epoch if it can't be converted by localtime.  This is better than
just saying "invalid", and is consistent with what "ls" does.
Don't dump core if the year has more than 48 digits; this isn't
possible on any contemporary host, but we might as well do it right.