Sockets facelift. APIs that could return binary data (e.g. aton() and

Sockets facelift. APIs that could return binary data (e.g. aton() and
recv()) now return bytes, not str or str8.  The socket.py code is
redone; it now subclasses _socket.socket and instead of having its own
_fileobject for makefile(), it uses io.SocketIO.  Some stuff in io.py
was moved around to make this work.  (I really need to rethink my
policy regarding readline() and read(-1) on raw files; and readline()
on buffered files ought to use peeking().  Later.)