When public access is used for the remote, it complained that the user
needed to set creds to use it, which was just wrong.
When creds were being used, it fell back from trying to use the version ID
to just accessing the key in the bucket, which was ok for non-export
remotes, but wrong for buckets.
In both cases, display a hopefully useful warning.
This should only come up when an existing S3 remote has been exported
to, and then later versioning was enabled.
Note that it would perhaps be possible to fall back from trying to use
retrieveKeyFile when it fails and instead use retrieveKeyFileFromExport,
which may work when S3 version ID is missing. But there are problems
with that approach; how to tell when retrieveKeyFile has failed due to this
rather than a network problem etc? Anyway, that approach would only work
until the file in the export got overwritten, and then it would no
longer be accessible. And with versioning enabled, the user wants old
versions of objects to remain accessible, so it seems better to warn
about the problem as soon as possible, so they can go back and add S3
version IDs.
This work is supported by the NIH-funded NICEMAN (ReproNim TR&D3) project.
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