Convert a MIME Entity to multipart/alternative

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Demonstrates the Chilkat Mime.ConvertToMultipartAlt method, which wraps the current entity in a new outer multipart/alternative, making the original the first child. It takes no arguments.

Note: The file paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: Use this to add an alternate rendering to an existing message — for example, promoting a plain-text message so an HTML version can be added alongside it. The original content becomes the first (least-preferred) alternative, and you append the richer representation after it. As with the mixed conversion, message-level headers move to the new outer entity.

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    success := false

    mime := chilkat.NewMime()
    success = mime.LoadMimeFile("qa_data/message.eml")
    if success == false {
        fmt.Println(mime.LastErrorText())
        mime.DisposeMime()
        return
    }

    //  Wrap the current entity in a new outer multipart/alternative entity.  The original entity
    //  becomes the first child, ready for an alternate representation to be added.
    success = mime.ConvertToMultipartAlt()
    if success == false {
        fmt.Println(mime.LastErrorText())
        mime.DisposeMime()
        return
    }

    //  Add an alternative representation of the same content.
    htmlPart := chilkat.NewMime()
    success = htmlPart.SetBodyFromHtml("<html><body>HTML alternative.</body></html>")
    if success == false {
        fmt.Println(htmlPart.LastErrorText())
        mime.DisposeMime()
        htmlPart.DisposeMime()
        return
    }

    success = mime.AppendPart(htmlPart)
    if success == false {
        fmt.Println(mime.LastErrorText())
        mime.DisposeMime()
        htmlPart.DisposeMime()
        return
    }

    fmt.Println("Number of parts: ", mime.NumParts())

    mime.DisposeMime()
    htmlPart.DisposeMime()