RFE: Prepare for transition to 64-bit (system) time

[jimklimov]

Y2K38 is just around the corner. Should stage some experiments in VMs clocked some 20 years ahead, see what breaks, fix up code for time64_t maths and printing (note: where available - e.g. maybe leave builds for very old platforms "as is", or provide fallback code to bring them up to spec practically).

Note: this may or may not concern times reported by, or settable on, the devices and their protocols in particular drivers. Primarily this is about having code that rubs shoulders with the OS ready for 64-bit timing reported by run-time calls (now=localtime(), time(&now), difftime*(), debug timestamps, hibernation sleeps, timers/alerts, etc. kind of stuff).