head, tail: More test.

* tests/head.test, tests/tail.test: Test if the option parser works.
dispatch: Add short option name.

* src/dctc/java/com/dataiku/dctc/command/Dispatch.java: Here.
dispatch: Update style and add some guidelines comments.

* src/dctc/java/com/dataiku/dctc/command/Dispatch.java: Here.
command: New help method for int parameter parsing.

* src/dctc/java/com/dataiku/dctc/command/abs/Command.java: With string
  as argument.
dispatch: Cache the command parsing.

* src/dctc/java/com/dataiku/dctc/command/Dispatch.java: Here.
dispatch: Use an enum instead of string.

* src/dctc/java/com/dataiku/dctc/command/Dispatch.java: Make the
  switch early.
dispatch: Fix end of command.

* src/dctc/java/com/dataiku/dctc/command/Dispatch.java: Need to bubble
  up when we have not a valid function.
dispatch: Fix error management.

* src/dctc/java/com/dataiku/dctc/command/Dispatch.java: The second one
  is just a drop of the content of the method. No needs to create the
  directory here.
dispatch: Delete meaningless print.

* src/dctc/java/com/dataiku/dctc/command/Dispatch.java: We don't need
  that.
dispatch: Display an error when needed.

* src/dctc/java/com/dataiku/dctc/command/Dispatch.java: Don't exit
  without print.
dispatch: Use explicitly the enum.

* src/dctc/java/com/dataiku/dctc/command/Dispatch.java: Here.
dispatch: Correct the default case of the switch.

* src/dctc/java/com/dataiku/dctc/command/Dispatch.java: An error
  appends before this point.