Fixes #16 Interference with remote checkpoint stored in sync gateway (#1987)
Fixes #16 Interference with remote checkpoint stored in sync gateway (#1987)

Add TestCheckpointsUniquePerReplication and implementation to pass test

SG ticket: couchbase/sync_gateway#1978
couchbaselabs/sync_gateway,paulharter/sync_gateway,ceejatec/sync_gateway,paulharter/sync_gateway,tophatch/sync_gateway,couchbaselabs/sync_gateway,ceejatec/sync_gateway,tophatch/sync_gateway,tophatch/sync_gateway,ceejatec/sync_gateway,tophatch/sync_gateway,couchbaselabs/sync_gateway,ceejatec/sync_gateway,couchbaselabs/sync_gateway,paulharter/sync_gateway,paulharter/sync_gateway