Johannes Schindelin [off-list ref] writes:

One notable fallout of this patch series is that on 64-bit Linux (and
other platforms where `unsigned long` is 64-bit), we now limit the range
of dates to LONG_MAX (i.e. the *signed* maximum value). This needs to be
done as `time_t` can be signed (and indeed is at least on my Ubuntu
setup).

Obviously, I think that we can live with that, and I hope that all
interested parties agree.

s/ulong/time_t/ is definintely a good change, and it will take us to
a place we would want to be in in some future.  

As long as there remains no platform we care about whose time_t and
long are still 32-bit signed integer, there will be a fallout to
them with this change.  Probably it is of a larger impact than
losing the upper half of a 64-bit timestamp range on larger boxes.
Hopefully those platforms have died out (or at least we don't mind
breaking them)?

It appears that we use uint64_t in many places in our code.  So
while philosophically time_t is the right type, uint64_t might be
practically a safer alternative type to use at the endgame patch in
this series.  I haven't seen it yet, but presumably the last one 6/6
is the endgame?