System call conversion for year 2038

Well, as was discussed in the email thread, anything that deals with inode time stamps has to use a 64-bit seconds value, and that is good enough for all practical uses. Using sub-nanosecond values for the fractional seconds would add very noticeable overhead with little benefit.

For interfaces that deal with timeouts (e.g. clock_nanosleep()), or current time (e.g. clock_gettime()), using unsigned 64-bit nanoseconds gives us until 2554, over 500 years before we have to come up with something else. If we can gain a noticeable performance improvement using the nanosecond based interface until then, it should be worth the effort.