fix some tests by making pointer types properly comparable and hashable, instead of relying on identity

partially reverted change that generally checked for None on object indexing - seems to trigger crashes in Py3.2 for some reason

disable GIL check on NoneCheckNode to avoid unnecessary output cluttering - if it fails, the operation it guards will (normally) also fail

minor code cleanups in metaclass utility code, fix compiler warning about unused function __Pyx_Py3MetaclassGet()