Add list command + test + test utils.
Move s3 error list to aybabtme/goamz
Tidy up interfaces with unique implementations.
Style changes.
printProgress builds string in steps.
Add a lock to List() to protect the *log.Logger.

In case someone tries to run two List at the same time.
Remove unecessary pointer references.
Typo.
Wrap mutable global in a type.
Add diff command.
Rename readNewList -> filterNewKeys.
Wrap mutable global in a type.