Encode a python int.

def _encode_int(name, value, dummy0, dummy1):
    """Encode a python int."""
    if -2147483648 <= value <= 2147483647:
        return b"\x10" + name + _PACK_INT(value)
    else:
        try:
            return b"\x12" + name + _PACK_LONG(value)
        except struct.error:
            raise OverflowError("BSON can only handle up to 8-byte ints")