Improve compatibility with python 2.6
Improve compatibility with python 2.6

dotsdl/PyTables,gdementen/PyTables,tp199911/PyTables,dotsdl/PyTables,rabernat/PyTables,PyTables/PyTables,avalentino/PyTables,rabernat/PyTables,FrancescAlted/PyTables,jennolsen84/PyTables,joonro/PyTables,jennolsen84/PyTables,andreabedini/PyTables,rabernat/PyTables,joonro/PyTables,avalentino/PyTables,andreabedini/PyTables,mohamed-ali/PyTables,mohamed-ali/PyTables,tp199911/PyTables,jack-pappas/PyTables,andreabedini/PyTables,rdhyee/PyTables,avalentino/PyTables,PyTables/PyTables,rdhyee/PyTables,jennolsen84/PyTables,PyTables/PyTables,gdementen/PyTables,rdhyee/PyTables,dotsdl/PyTables,jennolsen84/PyTables,tp199911/PyTables,gdementen/PyTables,jack-pappas/PyTables,andreabedini/PyTables,rdhyee/PyTables,rabernat/PyTables,FrancescAlted/PyTables,jack-pappas/PyTables,FrancescAlted/PyTables,jack-pappas/PyTables,joonro/PyTables,tp199911/PyTables,mohamed-ali/PyTables,jack-pappas/PyTables,gdementen/PyTables,joonro/PyTables,mohamed-ali/PyTables,dotsdl/PyTables