approximate Perspective.full within the bounds of the JVM;

--- a/src/Pure/PIDE/text.scala	Tue Feb 21 16:48:10 2012 +0100
+++ b/src/Pure/PIDE/text.scala	Tue Feb 21 17:08:32 2012 +0100
@@ -74,6 +74,8 @@
   {
     val empty: Perspective = Perspective(Nil)
 
+    def full: Perspective = Perspective(List(Range(0, Integer.MAX_VALUE / 2)))
+
     def apply(ranges: Seq[Range]): Perspective =
     {
       val result = new mutable.ListBuffer[Text.Range]