Problem: caller should own message returned by _recv
Problem: caller should own message returned by _recv

Solution: do not destroy in generated code; allow caller to do this.

This is more consistent with what we'd expect from a CLASS API and
does not cost anything in performance terms. Also since the caller
will usually consume the message in order to process it, it also
makes sense.

jdiez17/zproto,zeromq/zproto,sappo/zproto,bkmit/zproto,zeromq/zproto,sphaero/zproto,hintjens/zproto,zeromq/zproto,bkmit/zproto,somdoron/zproto,sphaero/zproto,vyskocilm/zproto,bkmit/zproto,asokoloski/zproto,jemc/zproto,asokoloski/zproto,somdoron/zproto,jemc/zproto,jdiez17/zproto,c-rack/zproto,sphaero/zproto,asokoloski/zproto,jdiez17/zproto,hintjens/zproto,c-rack/zproto,sappo/zproto,vyskocilm/zproto,somdoron/zproto,bkmit/zproto,vyskocilm/zproto,asokoloski/zproto,c-rack/zproto,somdoron/zproto,sappo/zproto,vyskocilm/zproto,hintjens/zproto,zeromq/zproto,vyskocilm/zproto,jemc/zproto,jemc/zproto,asokoloski/zproto,sappo/zproto,c-rack/zproto,sphaero/zproto,sappo/zproto,somdoron/zproto,hintjens/zproto,jemc/zproto,vyskocilm/zproto,jemc/zproto,bkmit/zproto,bkmit/zproto,hintjens/zproto,bkmit/zproto,jdiez17/zproto,sphaero/zproto,jdiez17/zproto,zeromq/zproto,sphaero/zproto,somdoron/zproto,zeromq/zproto,sappo/zproto,c-rack/zproto,jdiez17/zproto,vyskocilm/zproto,zeromq/zproto,asokoloski/zproto,jdiez17/zproto,somdoron/zproto,c-rack/zproto,hintjens/zproto,c-rack/zproto,sappo/zproto,asokoloski/zproto,jemc/zproto,hintjens/zproto