Better exception mapping

[Jeff Potts <jpotts@optaros.com>]

Regarding the exception handling in 3.2.4.1 Common CMIS Exceptions, I think we need better (more explicit?) status code/status message mapping here. The way it currently stands, a client app has no way of knowing the difference between a contentAlreadyExists (409) error and a versioning (also 409) error. People writing to a specific client can look at the error message to decide but that doesn't work for an interoperable client that can't predict the content of those messages.

Jeff