(ocaml) avoid extra conversion during multi-format data serialization
(ocaml) avoid extra conversion during multi-format data serialization

Do nothing if input_format = output_format during mutli-format data
serialization for OCaml (the same as for Erlang).

Motiejus/piqi-deb,Motiejus/piqi-deb,alavrik/piqi,Motiejus/piqi-deb,Motiejus/piqi-deb,alavrik/piqi,alavrik/piqi