CORS: respect specification regarding Access-Control-Allow-Headers

According to the specification, the value of the response header
Access-Control-Allow-Headers must contain at least all the values of the
request header Access-Control-Request-Headers to be considered a valid request.
Before this commit, only the Authorization value was present, which is enough
for Firefox but not for Chrome.
This should now work as expected.

library/server/ewsgi/specification/request/wgi_meta_names.e

@@ -50,6 +50,8 @@ feature -- Access
 
 	http_transfer_encoding: STRING = "HTTP_TRANSFER_ENCODING"
 
+	http_access_control_request_headers: STRING = "HTTP_ACCESS_CONTROL_REQUEST_HEADERS"
+
 	gateway_interface: STRING = "GATEWAY_INTERFACE"
 
 	auth_type: STRING = "AUTH_TYPE"