Fix inheritance in IsDescription classes (closes: gh-65)
Fix inheritance in IsDescription classes (closes: gh-65)

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