User-defined fault handler in decentralized coordination for indicatedTag <= currentTag

[hokeun]

We need to gracefully handle the error when the indicated tag from RTI is not in the future with respect to the current tag in the decentralized coordination, using a user-defined fault handler.

Thanks for the suggestion. I added this check in b99781d.

This fix will work for centralized coordination (where it is a hard error), but not for decentralized coordination, where it should lead to the invocation of a user-defined fault handler. We can create an issue for this and leave it out of this PR.

Originally posted by @lhstrh in #71 (comment)