* Add new switches:

* Add new switches:
    news-group-keep-seen-headers
    news-group-show-seen-headers

* Change default for news-group-show-context-headers.

* Change binding of news-toggle-online to shift-O.

* Change code that collapses and expands threads so that only those
  threads that need to be changed are actually rewritten.

* Add "B" marker in header lines to show which messages have
  associated bodies stored in the new body database.

* Add command news-read-marked-bodies (bound to "r") to read the
  marked bodies in a news-group buffer.

* Make noticeable change to the performance of header-parsing code, in
  order to support groups with very large numbers of headers.