Job serialization: add 32 bit total serialized len prefix.
Job serialization: add 32 bit total serialized len prefix.

This way it is trivial to concatenate multiple jobs into a single big
blob for message passing between nodes.

lamby/disque,GrimDerp/disque,jmptrader/disque,themage/disque,douxiaozhao/disque,sunheehnus/disque,seppo0010/disque,hanicker/disque,felixbuenemann/disque,chen-tian/disque,Koed00/disque,lamby/disque,ErikDubbelboer/disque,douxiaozhao/disque,jmptrader/disque,chen-tian/disque,gideonairex/disque,CodyReichert/disque,c2j/disque,ErikDubbelboer/disque,lamby/pkg-disque,antirez/disque,jmptrader/disque,gideonairex/disque,themage/disque,seppo0010/disque,mopuri-sandeep/disque,sunheehnus/disque,themage/disque,Koed00/disque,c2j/disque,tempbottle/disque,antirez/disque,CodyReichert/disque,hanicker/disque,GrimDerp/disque,tempbottle/disque,lamby/pkg-disque,mopuri-sandeep/disque,felixbuenemann/disque