Called whenever the selection has changed.

	// Simple example that lets you save the current selection and load it.
	
	class SelectionChange extends EditorWindow {
		var selectionIDs : int[];
		@MenuItem("Example/Selection Saver")
		static function Init() {
			var window = GetWindow(SelectionChange);
			window.Show();
		}
		function OnGUI() {
			if(GUILayout.Button("Save"))
				SaveSelection();
			if(GUILayout.Button("Load"))
				LoadLastSavedSelection();
		}
		function OnSelectionChange() {
			selectionIDs = Selection.instanceIDs;
		}
		function SaveSelection() {
			var saveStr = "";
			for(var i : int in selectionIDs)
				saveStr += i.ToString() + ";";
			saveStr = saveStr.TrimEnd(char.Parse(";"));
			EditorPrefs.SetString("SelectedIDs",saveStr);
		}
		function LoadLastSavedSelection() {
			var strIDs : String[] = EditorPrefs.GetString("SelectedIDs").Split(char.Parse(";"));
	
			var ids : int[] = new int[strIDs.Length];
			for(var i = 0; i < strIDs.Length; i++)
				ids[i] = parseInt(strIDs[i]);
			Selection.instanceIDs = ids;
		}
	}