[obcjarcopts] Encapsulate PtrState.RRI.KnownSafe in the methods PtrState.IsKnownSafe and PtrState.SetKnownSafe.

This is apart of a series of patches to encapsulate PtrState.RRI and
make PtrState.RRI a private field of PtrState.

*NOTE* This is actually the second commit in the patch stream. I should
have put this note on the first such commit r184528.