en assigned a default limit of 10 occurrences and timespan of 180 seconds, 
critical.txt would report the first 10 occurrences of a edm::LogError("thisID") message, and the first
10 occurrences of a edm::LogError("thatID") message.  After the 10 occurrences, an exponential backoff
kicks in.  After 180 seconds of no messages of that type, the count is reset, so that 10 more occurrences
could appear.

<p>
The <font color=red>PSet default = { ... }</font> parameter is optional.  If neither a default limit nor
