Fix error messaging to once again properly respond to specific S3 error status codes.
Just noticed on my local that the recent S3 plugin rewrite was logging errors differently. A simple cache miss (a common occurrence) has always been logged as an error. But the old S3 library produced a small one line output containing the status code. The new S3 library is extremely long in its output, which for a simple cache miss is way too much verbosity.
I've changed the error code to properly examine error status codes as reported by the new S3 library, and have made the "cache miss" case one that will only log a short info line.