a few other whitespace fixups
stable suite changes

* Avoid encoding the current stable suite in propellor's code,
  since that poses a difficult transition around the release,
  and can easily be wrong if an older version of propellor is used.
  Instead, the os property for a stable system includes the suite name
  to use, eg Stable "wheezy".
* stdSourcesList uses the stable suite name, to avoid unwanted
  immediate upgrades to the next stable release.
propellor spin