timestamp overflows sprinter interface

[Peter Wang]

Hi,

On a system where time_t is 64-bit and 'int' is a signed 32-bit integer
type, timestamps beyond some time in 2038 will be serialised to a
negative value.

The simplest solution appears to be to change the type in the sprinter
method to int64_t:

    void (*integer)(struct sprinter *, int64_t);

Any other suggestions?

Peter