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()

even when 'boundscheck' is disabled or indexing is trivial, call PyUnicode_READY() during unicode indexing to comply with C-API constraints

removed outdated dummy assignment code that originally prevented an unsed argument gcc warning for __pyx_self, fix one more case where __pyx_self needs to be marked as unused