git-annex 7.20190129 released with [[!toggle text="these changes"]]
[[!toggleable text="""
   * initremote S3: When configured with versioning=yes, either ask the user
     to enable bucket versioning, or auto-enable it when built with aws-0.22.
   * enableremote S3: Do not let versioning=yes be set on existing remote,
     because when git-annex lacks S3 version IDs for files stored in
     the bucket, deleting them would cause data loss.
   * S3: Detect when version=yes but an exported file lacks a S3 version ID,
     and refuse to delete it, to avoid data loss.
   * S3: Send a Content-Type header when storing objects in S3,
     so exports to public buckets can be linked to from web pages.
     (When git-annex is built with MagicMime support.)"""]]