Elaborate on what gets stored in pg_authid.rolpasswd.

Also, add cross-reference from pg_shadow.passwd to pg_authid.rolpasswd and
fix a bit of markup I muffed in my previous commit.

Per discussion with Josh Kupershmidt.

doc/src/sgml/catalogs.sgml

@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.229 2010/09/13 01:23:35 rhaas Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.230 2010/09/13 17:02:34 rhaas Exp $ -->
 <!--
  Documentation of the system catalogs, directed toward PostgreSQL developers
  -->
@@ -1179,7 +1179,14 @@
      <row>
       <entry><structfield>rolpassword</structfield></entry>
       <entry><type>text</type></entry>
-      <entry>Password (possibly encrypted); null if none</entry>
+      <entry>
+       Password (possibly encrypted); null if none.  If the password is
+       encrypted, this column will contain the string md5 followed by a
+       32-character hexadecimal MD5 hash.  The MD5 hash will be of the
+       user's password concatenated to their username (for example, if
+       user joe has password xyzzy, <productname>PostgreSQL</> will store
+       the md5 hash of xyzzyjoe).
+      </entry>
      </row>
 
      <row>
@@ -6938,7 +6945,7 @@
    <productname>PostgreSQL</productname> before version 8.1.
    It shows properties of all roles that are marked as
    <structfield>rolcanlogin</> in
-   <link linkend="catalog-pg-authid">pg_authid</link>.
+   <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.
   </para>
 
   <para>
@@ -7005,7 +7012,9 @@
       <entry><structfield>passwd</structfield></entry>
       <entry><type>text</type></entry>
       <entry></entry>
-      <entry>Password (possibly encrypted)</entry>
+      <entry>Password (possibly encrypted); null if none.  See
+      <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>
+      for details of how encrypted passwords are stored.</entry>
      </row>
 
      <row>