fix for #99491. persist mailnews sidebar height by persisting the outliner height.

r=varada, sr=mscott

mailnews/base/resources/content/mail3PaneWindowVertLayout.xul

@@ -151,7 +151,7 @@ Rights Reserved.
     <vbox flex="1">
       <hbox id="mail3PaneVertLayoutBox" persist="collapsed height" flex="1">
         <vbox id="folderPaneBox" flex="1" autostretch="always" persist="width">
-          <outliner id="folderOutliner" flex="1" style="width:0px;" context="folderPaneContext" persist="collapsed width"/>
+          <outliner id="folderOutliner" flex="1" style="width:0px;" context="folderPaneContext" persist="collapsed width height"/>
         </vbox>
         <splitter id="gray_vertical_splitter" collapse="before"  persist="state"/>
 

mailnews/base/resources/content/messenger.xul

@@ -148,7 +148,7 @@ Rights Reserved.
 
   <hbox style="height:100px" flex="1">
     <vbox id="sidebar-box">
-      <outliner id="folderOutliner" flex="1" context="folderPaneContext"/>
+      <outliner id="folderOutliner" persist="height width" flex="1" context="folderPaneContext"/>
     </vbox>
           
     <splitter id="sidebar-splitter"/>