Merge branch 'develop' of git://github.com/melinath/philo into develop

* 'develop' of git://github.com/melinath/philo:
  Added catch to NavigationManager.get_for_node for cases where items do not have a target node.
  Added a local cache to NavigationMapper - avoids some unpickling costs.
  Tweaked NavigationItem.is_active to better leverage the caching.
  Generalized the 'single step' case in TreeEntity.get_path to include the case where the root is the direct parent of the current instance.
  Forced path memoization prior to node caching for better performance.
  Added django cache backend use on top of cacheless shipherd.
  Corrections to has_navigation and navigation_host to use the new NavigationMapper correctly. Also added select_related calls to the NavigationManager.get_for_node method.
  Removed shipherd cache to see if it was really helping at all.
  Removed extraneous evaluations of TreeEntity.parent.
  Set handles_subpath to be a class method rather than trying to resolve the url based on instance data. Added a select_related depth of 1 to a node's view when trying to render it.
  Corrected a feed_patterns call in NewsletterView.urlpatterns.
  Minor optimization: only call patterns at the end of winer.FeedView.feed_patterns.
  Minor optimization to AttributeForm. Very slightly reduces the number of queries in the admin for Entities.
  Added memoization (optional but enabled by default) to TreeEntity.get_path.
  Eliminated (Generic)ForeignKey evaluations in shipherd's NavigationManager.update_cache_for, Node.accepts_subpath, and templatetages.nodes.NodeURLNode.render.
  Corrections to frozen models in migration 18 so that south knows what happened in 15-17.
  Eliminated unnecessary ContentType queries that used applabel/model-based lookups.
  Eliminated unnecessary ContentType queries from AttributeMapper._fill_cache.