Add missing throws.

* src/dctc/java/com/dataiku/dctc/command/Command.java (perform): Here.
main: More case for the help.

* src/dctc/java/com/dataiku/dctc/Main.java: Display the help message
  for help, -help, --help, -?, and -h.
Fix tail for S3.

* src/dctc/java/com/dataiku/dctc/file/S3File.java (getRange,
  getLastBytes): Here