OSF flag needs independent reset function.

[gerrygralton]

Current the OSF flag is reset in setSeconds() and no other function is provided to do it. This seems like a bit of an arbitrary choice and has led to some unpredictable errors occurring for me where this flag was being reset without me knowing how. The documentation says it makes good housekeeping sense and perhaps that's true but surely that should the user should at least be given the choice?

I propose that:

1. Clear OSF flag functionality should be removed from setSeconds().
2. Clear OSF flag function be defined independently to perform this role.