default with for single msg window is somehow more sane now (so we can see...

default with for single msg window is somehow more sane now (so we can see subject easier). fixes #1505

src/gtkgui.glade

@@ -15335,7 +15335,7 @@ Banner</property>
   <property name="type">GTK_WINDOW_TOPLEVEL</property>
   <property name="window_position">GTK_WIN_POS_NONE</property>
   <property name="modal">False</property>
-  <property name="default_width">400</property>
+  <property name="default_width">550</property>
   <property name="default_height">280</property>
   <property name="resizable">True</property>
   <property name="destroy_with_parent">False</property>