Add links to documentation from 9.1 release notes.

Author: bmomjian

doc/src/sgml/extend.sgml

@@ -354,7 +354,7 @@
     considered members of the extension.
    </para>
 
-   <sect2>
+   <sect2 id="extension">
     <title>Extension Files</title>
 
    <indexterm>

doc/src/sgml/func.sgml

@@ -1512,7 +1512,7 @@
       </row>
 
       <row>
-       <entry>
+       <entry id="format">
         <indexterm>
          <primary>format</primary>
         </indexterm>
@@ -9121,7 +9121,7 @@ SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
     </para>
    </sect3>
 
-   <sect3>
+   <sect3 id="xml-exists">
     <title>XMLEXISTS</title>
 
     <indexterm>
@@ -9163,7 +9163,7 @@ SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Tor
     </para>
    </sect3>
 
-   <sect3>
+   <sect3 id="xml-is-well-formed">
     <title>xml_is_well_formed</title>
 
     <indexterm>

doc/src/sgml/installation.sgml

@@ -2613,7 +2613,7 @@ cc-1020 cc: ERROR File = pqcomm.c, Line = 427
     buffering issues.
    </para>
 
-   <sect3>
+   <sect3 id="windows-crash-dumps">
     <title>Collecting Crash Dumps on Windows</title>
 
     <para>