Updating unpublished file needs fallback

[bpoldrack]

On JülichDATA trying to replace an unpublished file leads to an error.
This is an issue even in the most simple case, bc we need to push after a create-sibling, which implies replacing the repository files.

In this case, we'd need to remove the file and re-upload instead of using the replace endpoint.

Here is a snippet I have that used to fix _upload_file for this with an additional conditional when checking the response:

        elif response.status_code == 400 and \
                response.json()['status'] == "ERROR" and \
                "You cannot replace an unpublished file" in \
                response.json()['message']:
            # This happens on JülichDATA if we try to replace an unpublished
            # file. The message suggests to remote + upload instead.
            self._remove_file(key, remote_file)
            response = self.api.upload_datafile(identifier=self.doi,
                                                filename=local_file,
                                                json_str=datafile.json())

[bpoldrack]

@mih : We talked about how replace is only relevant for export mode, but I am once again not clear about datalad-annex remote helper. Those keys need replacement, I think. Note, that this is no difference from annex' POV with the current implementation, since it's transfer_store that detects the need for replacement here. If this fails, I think annex can't come up with its own workaround, b/c it can't tell that remove+transfer_store would work. So, this is different from renameexport.