Made json_array::clone() private.
Made json_array::clone() private.

Referer 053076f8e5091e0adb0963484cf5e960a3d722b0

takei-yuya/pficommon,retrieva/pficommon,pfi/pficommon,retrieva/pficommon,retrieva/pficommon,takei-yuya/pficommon,pfi/pficommon,pfi/pficommon,retrieva/pficommon,takei-yuya/pficommon,pfi/pficommon,takei-yuya/pficommon,retrieva/pficommon