Not quite sure how to handle this - part of the change was made so that useful error messages could actually be conveyed from methods. It may be basic permission, it may be missing information from a ticket update or a status change. That is why passing the full Trac error HTML page with just a status code is not a good solution - and particularly not as there are two different protocols (xml and json). Errors need better and differentiated handling.
What if we for XML passed the regular status code as fault code? So that a permission error would get a fault code of 403, and any non-specific error was 500?
I suppose I should re-read the spec again here...
