TST: against PyTables 3.1
rc1 revealed some bugs/API changes; hopefully this will not cause a need for an API change w.r.t 3.1

This may be a blocker for 0.13.1 (as may need to put in some checks for this)

https://github.com/PyTables/PyTables/issues/326

https://github.com/PyTables/PyTables/issues/327
