ITOH Yasufumi writes:
> Thus, I think there are no reason that the time_t shall not be
> an unsigned integer *from the standard*.

XPG makes it very clear that time_t is signed. As with off_t's, it
only says that it is an arithmetic type, but then goes on to say that
other types are unsigned, making it clear that "arithmetic type" means 
normal signed integer.

Perry