Doc: update external URLs for PostGIS project.

Paul Ramsey

doc/src/sgml/earthdistance.sgml

@@ -19,7 +19,7 @@
  <para>
   In this module, the Earth is assumed to be perfectly spherical.
   (If that's too inaccurate for you, you might want to look at the
-  <application><ulink url="http://www.postgis.org/">PostGIS</ulink></>
+  <application><ulink url="http://postgis.net/">PostGIS</ulink></>
   project.)
  </para>
 

doc/src/sgml/external-projects.sgml

@@ -231,7 +231,7 @@
    contains several extensions, which are described in
    <xref linkend="contrib">.  Other extensions are developed
    independently, like <application><ulink
-   url="http://www.postgis.org/">PostGIS</ulink></>.  Even
+   url="http://postgis.net/">PostGIS</ulink></>.  Even
    <productname>PostgreSQL</> replication solutions can be developed
    externally. For example, <application> <ulink
    url="http://www.slony.info">Slony-I</ulink></> is a popular

doc/src/sgml/release-8.4.sgml

@@ -6583,7 +6583,7 @@ WITH w AS (SELECT * FROM foo) SELECT * FROM w, bar ... FOR UPDATE
 
      <para>
       This is particularly useful for <ulink
-      url="http://postgis.refractions.net/">PostGIS</ulink>.
+      url="http://postgis.net/">PostGIS</ulink>.
      </para>
     </listitem>