containerutils: new Python-2.4 defaultdict

* Allows to use defaultdict with Python 2.4 as it comes
  with 2.5 and higher.

Signed-off-by: Patrick Glauner <patrick.oliver.glauner@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>
BibAuthorID: use defaultdict from containerutils

* Replaces local defaultdict backport with comprehensive
  one from containerutils.

Signed-off-by: Patrick Glauner <patrick.oliver.glauner@cern.ch>
Reviewed-by: Samuele Carli <samuele.carli@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>