GiST improvements:

- make sure we always invoke user-supplied GiST methods in a short-lived
  memory context. This means the backend isn't exposed to any memory leaks
  that be in those methods (in fact, it is probably a net loss for most
  GiST methods to bother manually freeing memory now). This also means
  we can do away with a lot of ugly manual memory management in the
  GiST code itself.

- keep the current page of a GiST index scan pinned, rather than doing a
  ReadBuffer() for each tuple produced by the scan. Since ReadBuffer() is
  expensive, this is a perf. win

- implement dead tuple killing for GiST indexes (which is easy to do, now
  that we keep a pin on the current scan page). Now all the builtin indexes
  implement dead tuple killing.

- cleanup a lot of ugly code in GiST

doc/src/sgml/gist.sgml

@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/gist.sgml,v 1.17 2005/04/09 03:52:43 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/gist.sgml,v 1.18 2005/05/17 00:59:30 neilc Exp $
 -->
 
 <chapter id="GiST">
@@ -202,7 +202,7 @@ $PostgreSQL: pgsql/doc/src/sgml/gist.sgml,v 1.17 2005/04/09 03:52:43 momjian Exp
  <para>
   The lack of write-ahead logging is just a small matter of programming,
   but since it isn't done yet, a crash could render a <acronym>GiST</acronym>
-  index inconsistent, forcing a REINDEX.
+  index inconsistent, forcing a <command>REINDEX</command>.
  </para>
 
 </sect1>