Fix Version/s: None
For DESC DC2 processing (at least!) there are reference catalogs that contain both unresolved (star) and resolved (galaxy) sources. For some purposes we want to be able to select out just the unresolved/stellar sources, and I imagine there could be other reference catalogs created in the future that are not pre-selected on stars.
Adding doUnresolved to the referenceSourceSelector can be done with ~5 lines of code + copying the appropriate test from ScienceSourceSelectorTaskTest.
Looks good. Feel free to ignore my comment if you like; just made it in case you considered it a mistake.