Detect and handle "windows" renewal requests

[oliwel]

When you create a new certificate request for an existing certificate this comes as a PKCS10 wrapped inside a PKCS7 container signed with the old certificate. As the file has the same PEM headers as a usual PKCS10 container is is not possible to distinguish this without parsing the data. To avoid any problems with such requests, the workflows should be able to transparently handle such uploads.