More detailed Exception

[maartenschermer]

I'm always frustrated when I try to download a non-existing file from iRODS and run into a general ValueError. For instance, if i'm downloading a list of objects, I want to have the option of distinguishing between "file not found" and other errors, so I can continue with downloading the rest of the files in the list, rather than having to fall back to a more general exception handler.

I would like a FileNotFoundError to be raised, rather than the current ValueError, when a file is not found.