minor SGML improvements

I've applied the attached patch to CVS. It makes a few minor SGML
markup improvements, and adds an additional cross-reference.

-Neil
Index: doc/src/sgml/ref/alter_domain.sgml
===================================================================
RCS file: /var/lib/cvs/pgsql-server/doc/src/sgml/ref/alter_domain.sgml,v
retrieving revision 1.11
diff -c -r1.11 alter_domain.sgml
*** a/doc/src/sgml/ref/alter_domain.sgml    29 Nov 2003 19:51:38 -0000    1.11
--- b/doc/src/sgml/ref/alter_domain.sgml    23 Mar 2004 13:02:15 -0000
***************
*** 139,145 ****
       </varlistentry>

       <varlistentry>
!       <term>CASCADE</term>
        <listitem>
         <para>
          Automatically drop objects that depend on the constraint.
--- 139,145 ----
       </varlistentry>

       <varlistentry>
!       <term><literal>CASCADE</literal></term>
        <listitem>
         <para>
          Automatically drop objects that depend on the constraint.
***************
*** 148,154 ****
       </varlistentry>

       <varlistentry>
!       <term>RESTRICT</term>
        <listitem>
         <para>
          Refuse to drop the constraint if there are any dependent
--- 148,154 ----
       </varlistentry>

       <varlistentry>
!       <term><literal>RESTRICT</literal></term>
        <listitem>
         <para>
          Refuse to drop the constraint if there are any dependent
***************
*** 174,184 ****
    <title>Examples</title>

    <para>
!    To add a NOT NULL constraint to a domain:
     <programlisting>
  ALTER DOMAIN zipcode SET NOT NULL;
     </programlisting>
!    To remove a NOT NULL constraint from a domain:
     <programlisting>
  ALTER DOMAIN zipcode DROP NOT NULL;
     </programlisting>
--- 174,184 ----
    <title>Examples</title>

    <para>
!    To add a <literal>NOT NULL</literal> constraint to a domain:
     <programlisting>
  ALTER DOMAIN zipcode SET NOT NULL;
     </programlisting>
!    To remove a <literal>NOT NULL</literal> constraint from a domain:
     <programlisting>
  ALTER DOMAIN zipcode DROP NOT NULL;
     </programlisting>
Index: doc/src/sgml/ref/cluster.sgml
===================================================================
RCS file: /var/lib/cvs/pgsql-server/doc/src/sgml/ref/cluster.sgml,v
retrieving revision 1.31
diff -c -r1.31 cluster.sgml
*** a/doc/src/sgml/ref/cluster.sgml    29 Nov 2003 19:51:38 -0000    1.31
--- b/doc/src/sgml/ref/cluster.sgml    23 Mar 2004 12:56:09 -0000
***************
*** 129,137 ****
     </para>

     <para>
!     Because the planner records statistics about the ordering of tables, it
!     is advisable to run <command>ANALYZE</command> on the newly clustered
!     table.  Otherwise, the planner may make poor choices of query plans.
     </para>

     <para>
--- 129,138 ----
     </para>

     <para>
!     Because the planner records statistics about the ordering of
!     tables, it is advisable to run <xref linkend="sql-analyze"
!     endterm="sql-analyze-title"> on the newly clustered table.
!     Otherwise, the planner may make poor choices of query plans.
     </para>

     <para>
***************
*** 175,181 ****
    </para>

    <para>
!    Cluster the <literal>employees</literal> relation using the same
     index that was used before:
  <programlisting>
  CLUSTER emp;
--- 176,182 ----
    </para>

    <para>
!    Cluster the <literal>employees</literal> table using the same
     index that was used before:
  <programlisting>
  CLUSTER emp;
Index: doc/src/sgml/ref/truncate.sgml
===================================================================
RCS file: /var/lib/cvs/pgsql-server/doc/src/sgml/ref/truncate.sgml,v
retrieving revision 1.16
diff -c -r1.16 truncate.sgml
*** a/doc/src/sgml/ref/truncate.sgml    29 Nov 2003 19:51:39 -0000    1.16
--- b/doc/src/sgml/ref/truncate.sgml    23 Mar 2004 13:05:23 -0000
***************
*** 60,67 ****
    </para>

    <para>
!    <command>TRUNCATE</> will not run any user-defined ON DELETE triggers
!    that might exist for the table.
    </para>
   </refsect1>

--- 60,67 ----
    </para>

    <para>
!    <command>TRUNCATE</> will not run any user-defined <literal>ON
!    DELETE</literal> triggers that might exist for the table.
    </para>
   </refsect1>

Index: doc/src/sgml/ref/vacuum.sgml
===================================================================
RCS file: /var/lib/cvs/pgsql-server/doc/src/sgml/ref/vacuum.sgml,v
retrieving revision 1.34
diff -c -r1.34 vacuum.sgml
*** a/doc/src/sgml/ref/vacuum.sgml    29 Nov 2003 19:51:39 -0000    1.34
--- b/doc/src/sgml/ref/vacuum.sgml    23 Mar 2004 13:06:18 -0000
***************
*** 64,77 ****
    </para>

    <para>
!    <command>FREEZE</command> is a special-purpose option that
     causes tuples to be marked <quote>frozen</quote> as soon as possible,
     rather than waiting until they are quite old.  If this is done when there
     are no other open transactions in the same database, then it is guaranteed
     that all tuples in the database are <quote>frozen</> and will not be
     subject to transaction ID wraparound problems, no matter how long the
     database is left unvacuumed.
!    <command>FREEZE</command> is not recommended for routine use.  Its only
     intended usage is in connection with preparation of user-defined template
     databases, or other databases that are completely read-only and will not
     receive routine maintenance <command>VACUUM</> operations.
--- 64,77 ----
    </para>

    <para>
!    <literal>FREEZE</literal> is a special-purpose option that
     causes tuples to be marked <quote>frozen</quote> as soon as possible,
     rather than waiting until they are quite old.  If this is done when there
     are no other open transactions in the same database, then it is guaranteed
     that all tuples in the database are <quote>frozen</> and will not be
     subject to transaction ID wraparound problems, no matter how long the
     database is left unvacuumed.
!    <literal>FREEZE</literal> is not recommended for routine use.  Its only
     intended usage is in connection with preparation of user-defined template
     databases, or other databases that are completely read-only and will not
     receive routine maintenance <command>VACUUM</> operations.