Unparenting BZ2File, as discussed in SF patch #661796.
(BZ2FileObject): Now the structure includes a pointer to a file object,
instead of "inheriting" one. Also, some members were copied from the
PyFileObject structure to avoid dealing with the internals of that
structure from outside fileobject.c.
These functions were adapted to the change above.
(BZ2File_seek,BZ2File_close): Use PyObject_CallMethod instead of
getting the function attribute locally.
(BZ2File_notsup): Removed, since it's not necessary anymore to overload
truncate(), and readinto() with dummy functions.
(BZ2File_methods): Added xreadlines() as an alias to BZ2File_getiter,
and removed truncate() and readinto().
Implemented getters for "newlines", "mode", and "name".
(BZ2File_init): Reworked to create a file instance instead of initializing
itself as a file subclass. Also, pass "name" object untouched to the
file constructor, and use PyObject_CallFunction instead of building the
argument tuple locally.
(BZ2File_Type): Set tp_new to PyType_GenericNew, tp_members to
BZ2File_members, and tp_getset to BZ2File_getset.
(initbz2): Do not set BZ2File_Type.tp_base nor BZ2File_Type.tp_new.
Do not mention that BZ2File inherits from the file type.