Don't require s3:// prefix on ls commands

The path will always refer to an s3 object,
so it's not necessary to specify s3://.  Now
we support both versions:

* aws s3 ls s3://bucket-name
* aws s3 ls bucket-name
Merge branch 's3-prefix-not-required' into develop

* s3-prefix-not-required:
  Don't require s3:// prefix on ls commands
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