more convenient get_font;

--- a/src/Pure/System/isabelle_system.scala	Mon May 10 17:07:47 2010 +0200
+++ b/src/Pure/System/isabelle_system.scala	Mon May 10 17:29:19 2010 +0200
@@ -318,8 +318,8 @@
 
   val font_family = "IsabelleText"
 
-  def get_font(bold: Boolean): Font =
-    new Font(font_family, if (bold) Font.BOLD else Font.PLAIN, 1)
+  def get_font(bold: Boolean = false, size: Int = 1): Font =
+    new Font(font_family, if (bold) Font.BOLD else Font.PLAIN, size)
 
   def install_fonts()
   {