Check `timeSinceOpen()` properly

[sembrestels]

From Sohkai's review: State.Funding state should still be present when _timeSinceOpen() == period (i.e. more correct as _timeSinceOpen() <= period).

[sembrestels]

If we change this check, many tests will fail, as at the end of the hatch period the state should be or Goal Reached or Refunding. I think changing this check changes the specification, and this could have unintended consequences.

Was changing this check a strong advice? Is it affecting something else than just the deadline in which somebody can contribute?