(gnus)Various Summary Stuff

`gnus-summary-mode-hook'
     This hook is called when creating a summary mode buffer.

`gnus-summary-generate-hook'
     This is called as the last thing before doing the threading and the
     generation of the summary buffer.  It's quite convenient for
     customizing the threading variables based on what data the
     newsgroup has.  This hook is called from the summary buffer after
     most summary buffer variables have been set.

`gnus-summary-prepare-hook'
     It is called after the summary buffer has been generated.  You
     might use it to, for instance, highlight lines or modify the look
     of the buffer in some other ungodly manner.  I don't care.

`gnus-summary-prepared-hook'
     A hook called as the very last thing after the summary buffer has
     been generated.

`gnus-summary-ignore-duplicates'
     When Gnus discovers two articles that have the same `Message-ID',
     it has to do something drastic.  No articles are allowed to have
     the same `Message-ID', but this may happen when reading mail from
     some sources.  Gnus allows you to customize what happens with this
     variable.  If it is `nil' (which is the default), Gnus will rename
     the `Message-ID' (for display purposes only) and display the
     article as any other article.  If this variable is `t', it won't
     display the article--it'll be as if it never existed.

`gnus-alter-articles-to-read-function'
     This function, which takes two parameters (the group name and the
     list of articles to be selected), is called to allow the user to
     alter the list of articles to be selected.

     For instance, the following function adds the list of cached
     articles to the list in one particular group:

          (defun my-add-cached-articles (group articles)
            (if (string= group "some.group")
                (append gnus-newsgroup-cached articles)
              articles))