Secondary input sources should not register anything when opening a file

Currently, input sources may insert objects into global registries when a new input file is opened.  This is OK for phase 1 of the multithreaded framework, except in the case of a secondary input source. This is because a secondary input source may open a new input file during any primary event.  This pull request modifies the ROOT/EDM input source so that it registers nothing if it is being used as a secondary input source.  This request does nothing for other input sources, but this is OK for now as the ROOT/EDM input source is the only source currently used for secondary input.