minor bug fix, define 'var' in dialog.js.

The 'cell' variable isn't defined and causes and error in the
console

IPython/html/static/base/js/dialog.js

@@ -1,84 +1,84 b''
 //----------------------------------------------------------------------------
 //  Copyright (C) 2013  The IPython Development Team
 //
 //  Distributed under the terms of the BSD License.  The full license is in
 //  the file COPYING, distributed as part of this software.
 //----------------------------------------------------------------------------
 
 //============================================================================
 // Utility for modal dialogs with bootstrap
 //============================================================================
 
 IPython.namespace('IPython.dialog');
 
 IPython.dialog = (function (IPython) {
     "use strict";
     
     var modal = function (options) {
         var dialog = $("<div/>").addClass("modal").attr("role", "dialog");
         dialog.append(
             $("<div/>")
                 .addClass("modal-header")
                 .append($("<button>")
                     .addClass("close")
                     .attr("data-dismiss", "modal")
                     .html("&times;")
                 ).append(
                     $("<h3/>").text(options.title || "")
                 )
         ).append(
             $("<div/>").addClass("modal-body").append(
                 options.body || $("<p/>")
             )
         );
         
         var footer = $("<div/>").addClass("modal-footer");
         
         for (var label in options.buttons) {
             var btn_opts = options.buttons[label];
             var button = $("<button/>")
                 .addClass("btn")
                 .attr("data-dismiss", "modal")
                 .text(label);
             if (btn_opts.click) {
                 button.click($.proxy(btn_opts.click, dialog));
             }
             if (btn_opts.class) {
                 button.addClass(btn_opts.class);
             }
             footer.append(button);
         }
         dialog.append(footer);
         // hook up on-open event
         dialog.on("shown", function() {
             setTimeout(function() {
                 footer.find("button").last().focus();
                 if (options.open) {
                     $.proxy(options.open, dialog)();
                 }
             }, 0);
         });
         
         // destroy dialog on hide, unless explicitly asked not to
         if (options.destroy == undefined || options.destroy) {
             dialog.on("hidden", function () {
                 dialog.remove();
             });
         }
         if (options.reselect_cell !== false) {
             dialog.on("hidden", function () {
                 if (IPython.notebook) {
-                    cell = IPython.notebook.get_selected_cell();
+                    var cell = IPython.notebook.get_selected_cell();
                     if (cell) cell.select();
                 }
             });
         }
         
         return dialog.modal(options);
     }
     
     return {
         modal : modal,
     };
 
 }(IPython));