Add attributes to core.time.abs.
Changed code coverage so that all lines line up in the lst file.
make TickDuration.currSystemTick nothrow

- The used functions only fail on invalid input,
  so any error is an implementation issue and assert
  should be used instead of throwing an exception.
Merge pull request #836 from jmdavis/abs

Add attributes to core.time.abs.
Merge pull request #834 from MartinNowak/currSystemTick_nothrow

make TickDuration.currSystemTick nothrow
Merge pull request #830 from economicmodeling/issue_4153

Issue 4153 Changed code coverage so that all lines line up in the lst file.