Start keeping track of the time since last contact for each client. Trigger...

Start keeping track of the time since last contact for each client.  Trigger the merger of histogram only if (as soon as) the average+2*sigma has passed since the last merge


git-svn-id: http://root.cern.ch/svn/root/trunk@41429 27541ba8-7e3a-0410-8455-c3a389f83636