update site fix (for installing 3.1 PDE, from "scratch")

org.eclipse.wtp.releng.webupdatesite/WebContent/site.xml

@@ -1300,5 +1300,7 @@
                  url="../../eclipse/updates/3.1/plugins/org.eclipse.jdt.launching.macosx_3.1.0.jar"/>
         <archive path="plugins/org.eclipse.jdt.junit.runtime_3.1.0.jar"
                  url="../../eclipse/updates/3.1/plugins/org.eclipse.jdt.junit.runtime_3.1.0.jar"/>
+       <archive path="plugins/org.eclipse.pde_3.1.0.jar"
+                 url="../../eclipse/updates/3.1/plugins/org.eclipse.pde_3.1.0.jar"/>
 
 </site>