It's unclear whether PyMarshal_XXX() are part of the public or private API.

They're named as if public, so I did a Bad Thing by changing
PyMarshal_ReadObjectFromFile() to suck up the remainder of the file in one
gulp:  anyone who counted on that leaving the file pointer merely at the
end of the next object would be screwed.  So restored
PyMarshal_ReadObjectFromFile() to its earlier state, renamed the new greedy
code to PyMarshal_ReadLastObjectFromFile(), and changed Python internals to
call the latter instead.