Change the package place for the PrettyString.

* src/dctc/java/com/dataiku/dctc/PrettyString.java: From here...
* src/core/java/com/dataiku/dip/output/PrettyString.java: ...to here.

* src/dctc/java/com/dataiku/dctc/configuration/Configuration.java,
  src/dctc/java/com/dataiku/dctc/configuration/CredentialProviderBank.java,
  src/dctc/java/com/dataiku/dctc/configuration/StructuredConf.java,
  src/dctc/java/com/dataiku/dctc/file/FileManipulation.java,
  src/dctc/java/com/dataiku/dctc/file/SshFile.java: Adjust compilation.
Clean clean target and create distclean target.

* build.xml (clean): Don't delete library directory.
* build.xml (distclean): Have the behavior of the previous clean
  target.