Feature Request #2227 option for compressing replication stream

Adds option to compress replication streams (off, lz4, pigz, plzip) and sets default to lz4.  In testing average of doubling of throughput and only scenario where adding lz4 compression could be detrimental was limited resource server, Gb+ network and low compressable data. More details are in ticket.

Pls note I have not been able to build release from source due (I think) to environmental issue but have build all archivers from ports without issue and had replication code running without error for a week so would now welcome wider testing