3710: update the combine_selected_files_into_collection method to also handle the scenarios where a collection uuid or "collection uuid/filename" is passed.
3710: handle the scenario where files from named collections are selected
3710: Refactored code to reduce redundancy.  Use select() to get the manifest
text instead of reloading each object for performance.
Merge branch '3710-combine-selections-bug' refs #3710