upgrade s3fs to support objects larger than 5GB

[jesteria]

Once this s3fs fix is released, we can update Triage's s3fs requirement, remove the S3Store open/write shim, and test Triage against it – as indicated by #687.

That PR's unit test should be preserved, and should pass, as a result of the update. It wouldn't be a bad idea to then run the PR's functional test, as well, to confirm.