Add some links to the CREATE FUNCTION reference page when describing

function definition for particular PLs. Original patch from David
Fetter, editorializing by Neil Conway.

doc/src/sgml/plperl.sgml

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-$PostgreSQL: pgsql/doc/src/sgml/plperl.sgml,v 2.39 2005/04/09 03:52:43 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/plperl.sgml,v 2.40 2005/05/20 01:52:24 neilc Exp $
 -->
 
  <chapter id="plperl">
@@ -44,7 +44,9 @@ $PostgreSQL: pgsql/doc/src/sgml/plperl.sgml,v 2.39 2005/04/09 03:52:43 momjian E
   <title>PL/Perl Functions and Arguments</title>
 
   <para>
-   To create a function in the PL/Perl language, use the standard syntax:
+   To create a function in the PL/Perl language, use the standard
+   <xref linkend="sql-createfunction" endterm="sql-createfunction-title">
+   syntax:
 <programlisting>
 CREATE FUNCTION <replaceable>funcname</replaceable> (<replaceable>argument-types</replaceable>) RETURNS <replaceable>return-type</replaceable> AS $$
     # PL/Perl function body

doc/src/sgml/plpython.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/plpython.sgml,v 1.28 2005/04/09 03:52:43 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/plpython.sgml,v 1.29 2005/05/20 01:52:25 neilc Exp $ -->
 
 <chapter id="plpython">
  <title>PL/Python - Python Procedural Language</title>
@@ -46,7 +46,9 @@
   <title>PL/Python Functions</title>
 
   <para>
-   Functions in PL/Python are declared in the usual way, for example
+   Functions in PL/Python are declared via the usual <xref
+   linkend="sql-createfunction" endterm="sql-createfunction-title">
+   syntax. For example:
 <programlisting>
 CREATE FUNCTION myfunc(text) RETURNS text
     AS 'return args[0]'

doc/src/sgml/pltcl.sgml

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-$PostgreSQL: pgsql/doc/src/sgml/pltcl.sgml,v 2.37 2005/04/09 03:52:43 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/pltcl.sgml,v 2.38 2005/05/20 01:52:25 neilc Exp $
 -->
 
  <chapter id="pltcl">
@@ -75,7 +75,9 @@ $PostgreSQL: pgsql/doc/src/sgml/pltcl.sgml,v 2.37 2005/04/09 03:52:43 momjian Ex
     <title>PL/Tcl Functions and Arguments</title>
 
     <para>
-     To create a function in the <application>PL/Tcl</> language, use the standard syntax:
+     To create a function in the <application>PL/Tcl</> language, use
+     the standard <xref linkend="sql-createfunction"
+     endterm="sql-createfunction-title"> syntax:
 
 <programlisting>
 CREATE FUNCTION <replaceable>funcname</replaceable> (<replaceable>argument-types</replaceable>) RETURNS <replaceable>return-type</replaceable> AS $$