Put message header and message pane in a box. r=hyatt.

mailnews/base/resources/content/messenger.xul

@@ -580,11 +580,12 @@ Rights Reserved.
 							 onclick="OnClickThreadAndMessagePaneSplitter()"/>
 			
       <!-- msg header view -->
+	  <box id="messagepanebox" align="vertical" flex="3">
       <toolbox id="msgHeaderView"/>
     
     	<!-- message view -->
-		  <html:iframe id="messagepane" flex="3" style="height:0px" name="messagepane" type="content-primary" src="about:blank"/>
-
+		  <html:iframe id="messagepane" style="height: 0px" flex="1" name="messagepane" type="content-primary" src="about:blank"/>
+	  </box>	
 		<box id="status-bar">
 		  <box align="vertical" style="width:100px">
 		    <spring flex="100%"/>