Update documentation to reflect that standard PLs are now extensions.

Recommend use of CREATE EXTENSION rather than plain CREATE LANGUAGE
where relevant.  Encourage PL authors to provide extension wrappers
for their PLs.

doc/src/sgml/plhandler.sgml

@@ -216,6 +216,15 @@ CREATE LANGUAGE plsample
     should execute this code and return.
    </para>
 
+   <para>
+    It's recommended that you wrap all these function declarations,
+    as well as the <command>CREATE LANGUAGE</> command itself, into
+    an <firstterm>extension</> so that a simple <command>CREATE EXTENSION</>
+    command is sufficient to install the language.  See
+    <xref linkend="extend-extensions"> for information about writing
+    extensions.
+   </para>
+
    <para>
     The procedural languages included in the standard distribution
     are good references when trying to write your own language handler.

doc/src/sgml/plperl.sgml

@@ -27,6 +27,7 @@
 
   <para>
    To install PL/Perl in a particular database, use
+   <literal>CREATE EXTENSION plperl</>, or from the shell command line use
    <literal>createlang plperl <replaceable>dbname</></literal>.
   </para>
 
@@ -967,8 +968,7 @@ $$ LANGUAGE plperl;
    mail.  To handle these cases, PL/Perl can also be installed as an
    <quote>untrusted</> language (usually called
    <application>PL/PerlU</application><indexterm><primary>PL/PerlU</></indexterm>).
-   In this case the full Perl language is available.  If the
+   In this case the full Perl language is available.  When installing the
-   <command>createlang</command> program is used to install the
    language, the language name <literal>plperlu</literal> will select
    the untrusted PL/Perl variant.
   </para>

doc/src/sgml/plpython.sgml

@@ -14,6 +14,7 @@
 
  <para>
   To install PL/Python in a particular database, use
+  <literal>CREATE EXTENSION plpythonu</>, or from the shell command line use
   <literal>createlang plpythonu <replaceable>dbname</></literal> (but
   see also <xref linkend="plpython-python23">).
  </para>

doc/src/sgml/pltcl.sgml

@@ -66,6 +66,7 @@
     directory if Tcl support is specified in the configuration step of
     the installation procedure.  To install <application>PL/Tcl</>
     and/or <application>PL/TclU</> in a particular database, use the
+    <command>CREATE EXTENSION</> command or the
     <command>createlang</command> program, for example
     <literal>createlang pltcl <replaceable>dbname</></literal> or
     <literal>createlang pltclu <replaceable>dbname</></literal>.

doc/src/sgml/ref/create_language.sgml

@@ -37,6 +37,21 @@ CREATE [ OR REPLACE ] [ TRUSTED ] [ PROCEDURAL ] LANGUAGE <replaceable class="pa
    defined in this new language.
   </para>
 
+  <note>
+   <para>
+    As of <productname>PostgreSQL</productname> 9.1, most procedural
+    languages have been made into <quote>extensions</>, and should
+    therefore be installed with <xref linkend="sql-createextension">
+    not <command>CREATE LANGUAGE</command>.  Direct use of
+    <command>CREATE LANGUAGE</command> should now be confined to
+    extension installation scripts.  If you have a <quote>bare</>
+    language in your database, perhaps as a result of an upgrade,
+    you can convert it to an extension using
+    <literal>CREATE EXTENSION <replaceable>langname</> FROM
+    unpackaged</literal>.
+   </para>
+  </note>
+
   <para>
    <command>CREATE LANGUAGE</command> effectively associates the
    language name with handler function(s) that are responsible for executing

doc/src/sgml/ref/drop_language.sgml

@@ -33,6 +33,15 @@ DROP [ PROCEDURAL ] LANGUAGE [ IF EXISTS ] <replaceable class="PARAMETER">name</
    previously registered procedural language.  You must be a superuser
    or the owner of the language to use <command>DROP LANGUAGE</>.
   </para>
+
+  <note>
+   <para>
+    As of <productname>PostgreSQL</productname> 9.1, most procedural
+    languages have been made into <quote>extensions</>, and should
+    therefore be removed with <xref linkend="sql-dropextension">
+    not <command>DROP LANGUAGE</command>.
+   </para>
+  </note>
  </refsect1>
 
  <refsect1>

doc/src/sgml/xplang.sgml

@@ -54,7 +54,7 @@
 
    <para>
     For the languages supplied with the standard distribution, it is
-    only necessary to execute <command>CREATE LANGUAGE</>
+    only necessary to execute <command>CREATE EXTENSION</>
     <replaceable>language_name</> to install the language into the
     current database.  Alternatively, the program <xref
     linkend="app-createlang"> can be used to do this from the shell
@@ -65,8 +65,7 @@
 createlang plperl template1
 </programlisting>
     The manual procedure described below is only recommended for
-    installing custom languages that <command>CREATE LANGUAGE</command>
+    installing languages that have not been packaged as extensions.
-    does not know about.
    </para>
 
    <procedure>
@@ -76,10 +75,10 @@ createlang plperl template1
 
     <para>
      A procedural language is installed in a database in five steps,
-     which must be carried out by a database superuser.  (For languages
+     which must be carried out by a database superuser.  In most cases
-     known to <command>CREATE LANGUAGE</>, the second through fourth steps
+     the required SQL commands should be packaged as the installation script
-     can be omitted, because they will be carried out automatically
+     of an <quote>extension</>, so that <command>CREATE EXTENSION</> can be
-     if needed.)
+     used to execute them.
     </para>
 
     <step performance="required" id="xplang-install-cr1">
@@ -136,14 +135,14 @@ CREATE FUNCTION <replaceable>inline_function_name</replaceable>(internal)
 CREATE FUNCTION <replaceable>validator_function_name</replaceable>(oid)
     RETURNS void
     AS '<replaceable>path-to-shared-object</replaceable>'
-    LANGUAGE C;
+    LANGUAGE C STRICT;
 </synopsis>
      </para>
     </step>
 
     <step performance="required" id="xplang-install-cr5">
      <para>
-      The PL must be declared with the command
+      Finally, the PL must be declared with the command
 <synopsis>
 CREATE <optional>TRUSTED</optional> <optional>PROCEDURAL</optional> LANGUAGE <replaceable>language-name</replaceable>
     HANDLER <replaceable>handler_function_name</replaceable>
@@ -154,7 +153,7 @@ CREATE <optional>TRUSTED</optional> <optional>PROCEDURAL</optional> LANGUAGE <re
       the language does not grant access to data that the user would
       not otherwise have.  Trusted languages are designed for ordinary
       database users (those without superuser privilege) and allows them
-      to safely create of functions and trigger
+      to safely create functions and trigger
       procedures. Since PL functions are executed inside the database
       server, the <literal>TRUSTED</literal> flag should only be given
       for languages that do not allow access to database server
@@ -201,7 +200,7 @@ CREATE FUNCTION plperl_inline_handler(internal) RETURNS void AS
     '$libdir/plperl' LANGUAGE C;
 
 CREATE FUNCTION plperl_validator(oid) RETURNS void AS
-    '$libdir/plperl' LANGUAGE C;
+    '$libdir/plperl' LANGUAGE C STRICT;
 </programlisting>
      </para>