Add process history map entry immediately on registration

There is a map from  ID of the full process history to the ID of the corresponding reduced process history that is stored in the ProcessHistoryRegistry, which is accessible across threads.  This map is currently filled in on demand, which means that the registry could be modified during any event, a problem for the multithreaded framework.
This pull request changes this so that an entry is inserted into the map when a process history is registered.  This means that the map will no longer, by itself, be a thread safety issue.  The ProcessHistoryRegistry as a whole is still an issue.