More error handling/reporting. Normalizing auth resp

Parses HTML reponses where XML were expected, for instance HTML pages
returned when domain is not found or HTML error pages from servlet
container when service-proxy app not found.

Also normalizes auth responses, renaming the document element 'response'
to 'auth' before handing the XML string to the parser (other responses
are named by their corresponding command, which is what the parser
expects). Thie original auth response is still preserved, though.