Need description for catch block arguments

[ericwinger]

As I understand it, if an RsrPromise catch block is invoked, the argument will be either a subclass of RsrAbstractReason or a subclass of RsrReasonService. The different types of reason do not have a consistent api.

In order to communicate information about the failure to the JfP user, I request that a description message be made for each type of reason and that it is guaranteed to return a string with as much information as possible.

Reference: GemTalk/JadeiteForPharo#386

[ericwinger]

It would also be helpful to include a tag message for consistency. Since tag is used by RCS/JfP to determine when an rsr process was intentionally terminated, we could eliminate a canUnderstand: send in JfP method,
RowanService>>#executeCommandOnCompletion: Probably could just return nil if the class doesn't have a concept of a tag.

[martinmcclure]

I'd suggest deprecating RsrAbstractReason and converting its subclasses to be RsrReasonServices, so the contract for a broken promise is always a kind of RsrReasonService.
And I agree that a #description message makes sense for all.