Timing funninesses

[David A. Moon <Moon at SCRC-TENEX>]

These are all a consequence of the 24-bit fixnum size, which means that
a positive fixnum only holds 8 seconds worth of microseconds.  There are
two time functions involved, one of which truncates the high end of the
32-bit microsecond clock (thus getting long-term accuracy at the cost of
having to be updated more often than every 4 seconds), and the other
truncates the low end of the 32-bit microsecond clock (thus being able
to go for an hour before it wraps around, but not having long-term
accuracy because it does an inexact division to convert to 60ths
of a second.)  The first of these does the left side of the wholine
and the second does the right side of the wholine.  The next Lisp machine
will of course do this better.