"Okay, then let's please call it:
_PyObject_Calloc(void *ctx, size_t nobjs, size_t objsize)
_PyObject_Alloc(int use_calloc, void *ctx, size_t nobjs, size_t objsize)"

"void * PyMem_RawCalloc(size_t nelem, size_t elsize);" prototype comes from the POSIX standad:
http://pubs.opengroup.org/onlinepubs/009695399/functions/calloc.html

I'm don't want to change the prototype in Python. Extract of Python documentation:

.. c:function:: void* PyMem_RawCalloc(size_t nelem, size_t elsize)

   Allocates *nelem* elements each whose size in bytes is *elsize* (...)