doc: Configure TOC generation in XSLT HTML build

The default table of contents in the XSLT HTML build is much too big and
deep.  Configure it to look more like the one that is currently being
produced by the DSSSL build.

doc/src/sgml/stylesheet.xsl

@@ -18,6 +18,7 @@
 <xsl:param name="link.mailto.url">pgsql-docs@postgresql.org</xsl:param>
 <xsl:param name="chunker.output.indent" select="'yes'"/>
 <xsl:param name="chunk.quietly" select="1"></xsl:param>
+<xsl:param name="toc.max.depth">2</xsl:param>
 
 
 <!-- Change display of some elements -->
@@ -38,4 +39,27 @@
   </span><br/>
 </xsl:template>
 
+
+<!-- table of contents configuration -->
+
+<xsl:param name="generate.toc">
+appendix  toc,title
+article/appendix  nop
+article   toc,title
+book      toc,title
+chapter   toc,title
+part      toc,title
+preface   toc,title
+qandadiv  toc
+qandaset  toc
+reference toc,title
+sect1     toc
+sect2     toc
+sect3     toc
+sect4     toc
+sect5     toc
+section   toc
+set       toc,title
+</xsl:param>
+
 </xsl:stylesheet>