No error message facility in adapter

[allanbowe]

The adapter provides a neat way to surface messages to the user (usermessage) or specific runtime issues (logmessage). It would be nice if a similar mechanism existed for returning an error message (eg errormessage). This would allow developers to use SAS side logic to gracefully surface a user friendly error message back to the front end - such as user Jim not found or unable to access xyz.