fix units on RescaleThreshold and initialize _nextScaleTime.

RescaleThreshold was being initialized to ns even though we were
comparing to ticks (100ns).

_nextScaleTime was not being initialized, so add that to Clear().
improve seeding of ThreadLocalRandom
add more timer tests, trying to replicate bug in upstream project
more tests.  trying to uncover meter infinity bug.
Merge branch 'master' into myget