Small updates to autodownloader configuration file maintenance.

- Add additional diangostics to server log and, on error, to the
  diagnostics IRC channel for administrative visibility.

- Correct wrong filename for moduledownloaderresources.xml.

- Move autodownloader update code into its own function.

- If the downloader XML couldn't be read or written, log an error
  but do not abort the script.

- Only attempt to rewrite the downloader XML if something changed.