SERVER-16197 Update docs/building.md for 2.8
SERVER-16291 allow index filters commands to run on secondaries if slaveOk explicitly set to true
SERVER-16032 SERVER-15957 Get OperationContext for ReplicationCoordinator::signalDrainComplete from the caller
SERVER-15986 SERVER-16283 improve validation to detect mmapv1 local.ns files
SERVER-15986 SERVER-16283 enable storage engine check