__TIME_MIN/__TIME_MAX

[Jacques A. Vidrine]

In at least one place in libc, it is necessary to range check a time_t
value.  One most platforms, time_t has the same range as `int', but
on at least amd64, it has a larger range.  Any objections to adding
definitions of __TIME_MIN and __TIME_MAX to sys/${arch}/_limits.h?

I could just do the usual check for lossage after casting, except that
in theory time_t could be a floating-point value (but not in reality
in FreeBSD).  It seems cleaner to me to have an explicit range.

Cheers,
-- 
Jacques Vidrine   NTT/Verio SME      FreeBSD UNIX       Heimdal
nectar at celabo.org jvidrine at verio.net nectar at freebsd.org nectar at kth.se