s3: try to create the bucket if the file doesn't exists.

* src/dctc/java/com/dataiku/dctc/file/S3File.java (mkdirs): Here.
When direct copy appends, don't forget to create the destination
directory. Closes: #17

* src/dctc/java/com/dataiku/dctc/copy/DirectCopyTaskRunnable.java: Here.
Missing throw.

* src/dctc/java/com/dataiku/dctc/command/Command.java: Here.