When an object is initialized with null bytes, do not overwrite the
PyObject_HEAD or PyObject_VAR_HEAD, which is initialized by Python
core function, e.g. PyObject_NEW().

New function EC_NewObject() is called for all object creations --
replacing four calls to either PyObject_NEW() or PyObject_NEW_VAR().
The new function initializes all the bytes that ExtensionClass is
resposible for and INCREFs the base class.

In ALLOC_FREE() macro, call _Py_NewReference() for objects allocated
from the free list.