Bug 236751 Add keyboard shortcuts to toggle the message pane and folder list r=rlk sr=bienvenu a=asa

suite/locales/en-US/chrome/common/help/shortcuts-mailnews.xhtml

@@ -35,6 +35,18 @@
     <td>F6</td>
     <td>F6</td>
   </tr>
+  <tr bgcolor="#eeeeee">
+    <td>Toggle Message Pane Visibility</td>
+    <td>F8</td>
+    <td>F8</td>
+    <td>F8</td>
+  </tr>
+  <tr>
+    <td>Toggle Folder Pane Visibility</td>
+    <td>F9</td>
+    <td>F9</td>
+    <td>F9</td>
+  </tr>
   <tr bgcolor="#eeeeee">
     <td>New Message</td>
     <td>Ctrl+M</td>