separate module "GUI", to keep this out of the way of generic Isabelle_System operations, notably for non-Isabelle/jEdit applications;
tuned signature;

--- a/src/Pure/System/gui_setup.scala	Thu Apr 04 17:33:04 2013 +0200
+++ b/src/Pure/System/gui_setup.scala	Thu Apr 04 17:47:28 2013 +0200
@@ -23,7 +23,7 @@
   }
 
   def top = new MainFrame {
-    iconImage = Isabelle_System.get_icon().getImage
+    iconImage = GUI.isabelle_image()
 
     title = "Isabelle setup"
 

--- a/src/Pure/System/isabelle_system.scala	Thu Apr 04 17:33:04 2013 +0200
+++ b/src/Pure/System/isabelle_system.scala	Thu Apr 04 17:47:28 2013 +0200
@@ -11,7 +11,6 @@
 import java.util.regex.Pattern
 import java.io.{File => JFile, BufferedReader, InputStreamReader,
   BufferedWriter, OutputStreamWriter}
-import javax.swing.ImageIcon
 
 import scala.util.matching.Regex
 
@@ -421,10 +420,4 @@
       case None => Isabelle_System.getenv_strict("ISABELLE_LOGIC")
     }
   }
-
-
-  /* icon */
-
-  def get_icon(): ImageIcon =
-    new ImageIcon(platform_path(Path.explode("~~/lib/logo/isabelle.gif")))
 }

--- a/src/Pure/Tools/build_dialog.scala	Thu Apr 04 17:33:04 2013 +0200
+++ b/src/Pure/Tools/build_dialog.scala	Thu Apr 04 17:47:28 2013 +0200
@@ -64,7 +64,7 @@
     more_dirs: List[(Boolean, Path)],
     session: String): MainFrame = new MainFrame
   {
-    iconImage = Isabelle_System.get_icon().getImage
+    iconImage = GUI.isabelle_image()
 
 
     /* GUI state */

--- a/src/Pure/Tools/ml_statistics.scala	Thu Apr 04 17:33:04 2013 +0200
+++ b/src/Pure/Tools/ml_statistics.scala	Thu Apr 04 17:47:28 2013 +0200
@@ -134,7 +134,7 @@
     ML_Statistics.standard_fields.map(chart(_)).foreach(c =>
       Swing_Thread.later {
         new Frame {
-          iconImage = Isabelle_System.get_icon().getImage
+          iconImage = GUI.isabelle_image()
           title = name
           contents = Component.wrap(new ChartPanel(c))
           visible = true

--- a/src/Pure/Tools/task_statistics.scala	Thu Apr 04 17:33:04 2013 +0200
+++ b/src/Pure/Tools/task_statistics.scala	Thu Apr 04 17:47:28 2013 +0200
@@ -53,7 +53,7 @@
   def show_frame(bins: Int = 100): Unit =
     Swing_Thread.later {
       new Frame {
-        iconImage = Isabelle_System.get_icon().getImage
+        iconImage = GUI.isabelle_image()
         title = name
         contents = Component.wrap(new ChartPanel(chart(bins)))
         visible = true

--- a/src/Pure/build-jars	Thu Apr 04 17:33:04 2013 +0200
+++ b/src/Pure/build-jars	Thu Apr 04 17:47:28 2013 +0200
@@ -42,6 +42,7 @@
   System/color_value.scala
   System/command_line.scala
   System/event_bus.scala
+  System/gui.scala
   System/gui_setup.scala
   System/html5_panel.scala
   System/interrupt.scala

--- a/src/Tools/Graphview/src/graphview.scala	Thu Apr 04 17:33:04 2013 +0200
+++ b/src/Tools/Graphview/src/graphview.scala	Thu Apr 04 17:47:28 2013 +0200
@@ -37,7 +37,7 @@
       catch { case exn: Throwable => println(Exn.message(exn)); sys.exit(1) }
 
     val top = new MainFrame {
-      iconImage = Isabelle_System.get_icon().getImage
+      iconImage = GUI.isabelle_image()
 
       title = "Graphview"
       minimumSize = new Dimension(640, 480)