more convenient look-and-feel setup;

--- a/src/Pure/System/gui_setup.scala	Mon May 10 17:29:19 2010 +0200
+++ b/src/Pure/System/gui_setup.scala	Mon May 10 17:37:32 2010 +0200
@@ -6,8 +6,6 @@
 
 package isabelle
 
-import javax.swing.UIManager
-
 import scala.swing._
 import scala.swing.event._
 
@@ -16,7 +14,7 @@
 {
   def startup(args: Array[String]) =
   {
-    UIManager.setLookAndFeel(Platform.look_and_feel)
+    Platform.init_laf()
     top.pack()
     top.visible = true
   }

--- a/src/Pure/System/platform.scala	Mon May 10 17:29:19 2010 +0200
+++ b/src/Pure/System/platform.scala	Mon May 10 17:37:32 2010 +0200
@@ -58,12 +58,14 @@
   private def find_laf(name: String): Option[String] =
     UIManager.getInstalledLookAndFeels().find(_.getName == name).map(_.getClassName)
 
-  def look_and_feel(): String =
+  def get_laf(): String =
   {
     if (is_windows || is_macos) UIManager.getSystemLookAndFeelClassName()
     else
       find_laf("Nimbus") orElse find_laf("GTK+") getOrElse
       UIManager.getCrossPlatformLookAndFeelClassName()
   }
+
+  def init_laf(): Unit = UIManager.setLookAndFeel(get_laf())
 }