BibField: Python-2.4 compliance

Signed-off-by: Esteban J. G. Gabancho <esteban.gabancho@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>
BibField: fix for lxml compatibility

Tested-by: Tibor Simko <tibor.simko@cern.ch>
Merge branch 'master' into next

* master:
  BibField: fix for lxml compatibility
  BibField: Python-2.4 compliance