Update 9.1 release notes to reflect commits through today.

Also do some desultory copy-editing on the notes.

Author: tglsfdc

doc/src/sgml/extend.sgml

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