cxxll::bounded_ordered_queue: Move common code to a new base class
cxxll::bounded_ordered_queue_unregister: New class
symboldb_download_repo: Use cxxll::bounded_ordered_queue_unregister
cxxll::bounded_ordered_queue test: Use bounded_ordered_queue_unregister
cxxll::queue_aborted: New class
cxxll::bounded_ordered_queue::abort(): New member function
cxxll::parallel::rethrow_first(): New member function
symboldb_download_repo: Abort queue on RPM load failure
symboldb_download_repo: Report the first thrown exception