[FEATURE] Ability to switch content packs so that vendors can offer regional content.

Original patch from jbetak@netscape.com, r=ben@netscape.com, sr=hyatt@netscape.com,
a=blizzard@mozilla.org
preftree.xul - add id to appearance treechildren to allow dynamically overlayed panels

xpfe/components/prefwindow/resources/content/preftree.xul

@@ -48,7 +48,7 @@
       <treerow>   
         <treecell class="treecell-indent" url="chrome://communicator/content/pref/pref-appearance.xul" label="&appear.label;"/> 
       </treerow>
-      <treechildren>
+      <treechildren id="appearanceChildren">
         <treeitem>
           <treerow>
             <treecell class="treecell-indent" url="chrome://communicator/content/pref/pref-fonts.xul" label="&fonts.label;"/> 
@@ -59,7 +59,7 @@
             <treecell class="treecell-indent" url="chrome://communicator/content/pref/pref-colors.xul" label="&colors.label;"/> 
           </treerow>
         </treeitem>
-        <treeitem>
+        <treeitem id="themes-panel">
           <treerow>
             <treecell class="treecell-indent" url="chrome://communicator/content/pref/pref-themes.xul" label="&themes.label;"/> 
           </treerow>