read proper snapshot for downstreamop generation
remove unused code
Fix dialyzer problem
Remove unnecessary lager info; add type for index_node; fix bug for empty list
Remove more lager info
Remove lager; fix 'exported from case'
Fix definition of index_node
Merge branch 'origin/downstreamop'

Conflicts:
	src/clocksi_downstream.erl
	src/clocksi_downstream_generator_vnode.erl
	src/clocksi_interactive_tx_coord_fsm.erl
	src/clocksi_tx_coord_fsm.erl
	src/clocksi_vnode.erl
	src/vectorclock.erl
remove unnecessary lager messages
provide transaction record instead of txid
error handling in prepare/commit