rrepair, merkle: apply techniques from r7273
rrepair, merkle: apply techniques from r7273

this reduces trivial RC costs (2nd merkle phase) by up to 50% when items have to be regenerated
scalaris-team/scalaris,caijieming-baidu/scalaris,jvf/scalaris,jvf/scalaris,scalaris-team/scalaris,scalaris-team/scalaris,scalaris-team/scalaris,caijieming-baidu/scalaris,jvf/scalaris,caijieming-baidu/scalaris,caijieming-baidu/scalaris,scalaris-team/scalaris,jvf/scalaris,jvf/scalaris,jvf/scalaris,scalaris-team/scalaris,scalaris-team/scalaris,scalaris-team/scalaris,caijieming-baidu/scalaris,caijieming-baidu/scalaris,jvf/scalaris,caijieming-baidu/scalaris