Explicitly state the location of the Content-ID header in a change set

Although the examples are clear where the Content-ID header should go in a change set, the text is not. The multipart spec (RFC 2045 and 2046), do show that the Content-ID header is a MIME-part-header but it doesn't exclude it from being used in other places (consider the Content-Type header which is used both in the MIME-part-header and part of the OData request).