convert: raise Abort instead of NoRepo when CVS pserver auth fails.
At this point we know the source is CVS, so we should not go through
the rest of the converters.
abort: repository a not found!
255
abort: error: Connection refused
255
abort: repository a not found!
255
abort: destination '../a' already exists
255
abort: repository a not found!
255
destination directory: q
abort: destination 'q' already exists