2038: only 21 years away

I checked the nfsv3 code again and had indeed misremembered what Linux does: the timestamp is interpreted as unsigned on 64-bit machines today, so we are good until 2106 in theory.

The problem is nfsv3 implementations that treat the timestamp as signed, and that includes today's 32-bit linux kernels, and probably half of the other implementations (file system implementors elsewhere have been relatively random in their interpretation of time stamps being either signed or unsigned).