Add a test for indexing columns containing a nan in the first row.
Add a test for indexing columns containing a nan in the first row.

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