Do not assume that INTERNAL-TIME-UNITS-PER-SECOND is 1000

[kenoss]

c.f. http://www.ai.mit.edu/projects/iiip/doc/CommonLISP/HyperSpec/Body/fun_get-internal-real-time.html

[kenoss]

https://github.com/cxxxr/lem/blob/master/lib/core/timer.lisp

I mean timer-ms seems to be intended for ms but we can not assume that get-internal-real-time returns ms.