Unparenting BZ2File, as discussed in SF patch #661796.

* Modules/bz2module.c
  (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.

  (Util_GetLine,Util_DropReadAhead,Util_ReadAhead,Util_ReadAheadGetLineSkip,
   BZ2File_write,BZ2File_writelines,BZ2File_init,BZ2File_dealloc,
   BZ2Comp_dealloc,BZ2Decomp_dealloc):
   	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().

  (BZ2File_get_newlines,BZ2File_get_closed,BZ2File_get_mode,BZ2File_get_name,
   BZ2File_getset):
   	Implemented getters for "newlines", "mode", and "name".

  (BZ2File_members): Implemented "softspace" member.

  (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.


* Doc/lib/libbz2.tex
  Do not mention that BZ2File inherits from the file type.

Doc/lib/libbz2.tex

@@ -23,8 +23,6 @@ Here is a resume of the features offered by the bz2 module:
 \item \class{BZ2File} class implements universal newline support;
 \item \class{BZ2File} class offers an optimized line iteration using
       the readahead algorithm borrowed from file objects;
-\item \class{BZ2File} class inherits from the builtin file type
-      (\code{issubclass(BZ2File, file)} is \code{True});
 \item Sequential (de)compression supported by \class{BZ2Compressor} and
       \class{BZ2Decompressor} classes;
 \item One-shot (de)compression supported by \function{compress()} and