enabled few tests for gae, close web2py/web2py#729, limitby seems to work now
enabled few tests for gae, close web2py/web2py#729, limitby seems to work now

niphlod/pydal,willimoa/pydal,web2py/pydal,manuelep/pydal,stephenrauch/pydal,michele-comitini/pydal,kmcheung12/pydal