NOJIRA:  Enhancements to logging & error handling related to how DLM dec...

...ides whether a user receives a fragment;  should make troubleshooting much clearer

When issues occur, the current code produces stack traces in the logs that don't name fragments, groups, or user accounts.  These omissions make it hard to narrow your search for the cause of an issue, such as a missing group.
The new `RuntimeException should wrap `e` so as to retain whatever detail might have been available from the caught `Exception`.