makes new hash the default, with an opt-out (& js-no-big-int) define.
Also update changelog (& fix one typo).
Only really expect the chronos hash-order sensitive test to fail until
they merge that PR and tag a new release.
* clean up some test categories
* mention exact slice issue
* magics into system
* move trangechecks into overflow
* move tmemory to system
* try fix CI
* try fix CI
* final CI fix
