adding scaling of scoring based on max_lag_secs, added compatability for different 'optime' fields
adding scaling of scoring based on max_lag_secs, added compatability for different 'optime' fields

Percona-Lab/mongodb_consistent_backup,timvaillancourt/mongodb_consistent_backup,timvaillancourt/mongodb_consistent_backup,Percona-Lab/mongodb_consistent_backup,timvaillancourt/mongodb_consistent_backup,Percona-Lab/mongodb_consistent_backup