LC Comment: Supported faults

There are currently SOAP faults for

    * Invalid Message Addressing Property
    * Message Addressing Property Required
    * Destination Unreachable
    * Action Not Supported
    * Endpoint Unavailable

In the "Invalid message addressing property" the distinction of whether 
the fault is syntactic or semantic is left to the [Reason] text, which 
we don't specify normatively.  Recovery may differ significantly for 
these two cases, and it would be better to be able to distinguish them 
easily in a standard way.  There are several other distinctions that we 
can see may occur, based on the current definitions, but do not 
distinguish in a standard way.

The set of faults should be expanded to include

    * Invalid Message Addressing Property Syntax (semantic errors
      continue to use "Invalid Message Addressing Property")
    * Unknown Relationship Type ([relationship] contained an entry with
      an unknown relation IRI)
    * Duplicate Reply Relation ([relationship] contained more than one
      reply relation entry)
    * Duplicate Message Addressing Property (multiple versions of the
      same header targeted at a given node).
    * Duplicate Message ID (assuming this is to be enforced, an endpoint
      can at least say that it has received distinct messages with the
      same ID)

There may be others, as well.