Miscutil: new defaultdict Python 2.4 backport

 * 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>
BibAuthorID: use Miscutil defaultdict

 * Replaces local defaultdict backport with comprehensive
   one in Miscutil

Signed-off-by: Patrick Glauner <patrick.oliver.glauner@cern.ch>