Merge branch 'fix/25-return-508-loop-detected' into 'master'

[Context Source]{.HTML-Keyboard} are in turn reliant on previously encountered

[Context Sources]{.HTML-Keyboard} thus causing an infinite loop. Therefore, when

processing a distributed operation, a specific field listing all previously

encountered [Context Sources]{.HTML-Keyboard} (e.g. a Via header in the response

in case of HTTP binding (IETF RFC 7230 [n.12])) shall be passed as part of the

request and this field can be used to exclude duplicated sources from matching

as [Context Source Registration]{.HTML-Keyboard}.

encountered [Context Sources]{.HTML-Keyboard} (e.g. a [Via]{.HTML-Code} header 

in the response in case of HTTP binding (IETF RFC 7230 [n.12])) shall be passed

as part of the request and this field can be used to exclude duplicated sources 

from matching as [Context Source Registration]{.HTML-Keyboard}. If the requested 

endpoint is also listed as **previously encountered** when a

[Context Source]{.HTML-Keyboard} receives a call to that endpoint, this is an

indication that a new loop has been detected. A suitable error shall be returned,

indicating that the loop has been detected.

In the case of multi-tenancy (see Clause+++clause-7+++7.8) each

[Tenant]{.HTML-Keyboard} found within each registered [Context