Adding support for echoing the request origin for CORS.

Motivation:
When CORS has been configured to allow "*" origin, and at the same time
is allowing credentials/cookies, this causes an error from the browser
because when the response 'Access-Control-Allow-Credentials' header
is true, the 'Access-Control-Allow-Origin' must be an actual origin.

Modifications:
Changed CorsHandler setOrigin method to check for the combination of "*"
origin and allowCredentials, and if the check matches echo the CORS
request's 'Origin' value.

Result:
This addition enables the echoing of the request 'Origin' value as the
'Access-Control-Allow-Origin' value when the server has been configured
to allow any origin in combination with allowCredentials.

This allows client requests to succeed when expecting the server to
be able to handle "*" origin and at the same time be able to send cookies
by setting 'xhr.withCredentials=true'. A concrete example of this is
the SockJS protocol which expects behaviour.