Cluster summary rewrite

The ClusterSummary and ClusterSummaryProducer classes were updated to improve performance, as documented here:

https://its.cern.ch/jira/browse/CMSTRACK-51
(https://indico.cern.ch/event/322710/session/5/contribution/2/material/slides/1.pdf)
Automatically ported from CMSSW_7_2_X #5136
I don't see anywhere in this method where other than -1 is returned. This is a bug
I'd expect instead of the last 5 lines to see
```
if (warn && iM==-1) edmLogWarning...
return iM;
```