Pharo class RsrConnectionClosedBeforeReceivingResponse should be a subclass of Error

[ericwinger]

A RsrPromise block catch: block can get a RsrConnectionClosedBeforeReceivingResponse. However, RsrConnectionClosedBeforeReceivingResponse is a subclass of RsrAbstractReason not Error. Since the client is effective dead, I think this should be an error to tell the client (and consequently the user) to take more aggressive recovery action.

[ericwinger]

I suppose it would be more proper to request that the class become a subclass of RsrRemoteException