merkle: only send RC pid when sending the merkle_tree root
merkle: only send RC pid when sending the merkle_tree root

(the RC process will not change afterwards!)
-> saves ~51 bytes per message
digshock/scalaris,seyyed/scalaris,seyyed/scalaris,seyyed/scalaris,digshock/scalaris,seyyed/scalaris,tectronics/scalaris,digshock/scalaris,digshock/scalaris,tectronics/scalaris,digshock/scalaris,digshock/scalaris,tectronics/scalaris,tectronics/scalaris,tectronics/scalaris,tectronics/scalaris,seyyed/scalaris,seyyed/scalaris,tectronics/scalaris,seyyed/scalaris,digshock/scalaris