* Add preview parameter to preprocesser calls, use this rather than the

* Add preview parameter to preprocesser calls, use this rather than the
  previous ugly hack used to avoid writing rss feeds in previews.
* Fix the img plugin to avoid overwriting images in previews. Instead it
  does all the work to make sure the resizing works, and dummys up a resized
  image using width and height attributes.
* Also fixes img preview display, the links were wrong in preview before.