This commit changes the node_delete() API.  A list of affected modules is available at http://drupal.org/node/36250#comment-52963.

- Emit charset for blogapi RSD

  TODO:
  + The contact.module was broken; a new patch for contact.module is needed.
  + Documentation is needed.
  + The most important modules need to be updated ASAP.

All node revisions were stored in a serialized field in the node table and retrieved for _each_ page view although they are rarely needed. We created a separate revisions table which would be in principle identical to the node table, only that it could have several old copies of the same node.  This also allows us to revision-related information, and to provide log entries to non-book pages when a new revision is being created.

TODO:

1. Provide upgrade instructions for node module maintainers!
2. Upgrade modules that implement node types.
3. Provide an upgarde path for revisions.  Dependency on the upgrade system.

  part of the node system!  If you have a module that implements node
  types, you'll have to udpate its CVS HEAD version.

  We replaced _node_name() and _node_types() by _node().  The new _node()
  hook let's you define one or more node types, including their names.
  The implementation of the _node() hook needs to:

   return array($type1 => array('name' => $name1, 'base' => $base1),
                $type2 => array('name' => $name2, 'base' => $base2));

  where $type is the node type, $name is the human readable name of the type
  and $base is used instead of <hook> for <hook>_load, <hook>_view, etc.

  For example, the story module's node hook looks like this:

    function story_node() {
      return array('story' => array('name' => t('story'), 'base' => 'story'));
    }

  The page module's node hook module like:

    function page_node() {
      return array('page' => array('name' => t('page'), 'base' => 'page'));
    }

  However, more complex node modules like the project module and the
  flexinode module can use the 'base' parameter to specify a different base.

  The project module implements two node types, proejcts and issues, so it
  can do:

    function project_node() {
      return array(
       array('project_project' => array('name' => t('project'), 'base' => 'project'),
       array('project_issue' => array('name' => t('issue'), 'base' => 'project_issue'));
    }

  In the flexinode module's case there can only one base ...

  This hook will simplify the CCK, and will make it easy (or easier) to merge
  the story and page module.

  In addition, node_list() became node_get_types().  In addition, we created
  the following functions: node_get_name($type) and node_get_base($type).

  TODO: update documentation!

  TODO: update migration page in handbook.

- Code cleanup: improve format_plural usage, add some missing placeholder/check calls, and introduce API for <link> tags.

- Patch #19451 by JonBob: improved consistency of module descriptions.  We should write guidelines for this -- maybe in the PHPDoc code of the _help hook.

  We added a 'severity' column to watchdog():
    watchdog($type, $message, $link) --> watchdog($type, $message, $severity, $link);

    * Specify a severity in case you are reporting a warning or error.
    * The $link-parameter is now the fourth parameter instead of the third.

  TODO: document this in the upgrade guide.

- Patch by James: made the blogapi module work again.

- Patch #11682: changed FILTER_DEFAULT_FORMAT to FILTER_FORMAT_DEFAULT to make the Blog API work.

   + Made error strings in blog.module consistent.
   + Explained a bit better what the RSD setting is for in the blog module.
   + Removed the notes about PHP content from block module and book module, since everything is handled via the input formats now.