fixes unicode comparison warning.
fixes unicode comparison warning.

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