The :mod:`pickle` C accelerator now enforces frame boundaries when
unpickling, as the pure Python implementation already did.  An argument that
straddles a frame boundary, or a frame that begins before the previous one has
ended, now raises :exc:`pickle.UnpicklingError` instead of
being silently read across the boundary.  This prevents the loaded data from
diverging from the :mod:`pickletools` disassembly of the same pickle.
