title: Selective history.back() using Backbone.js
body: <p>I have a Backbone app.  I'm using Backbone.history to enable use of the back button.  We have a page (settings) that auto loads a popup requiring input from the user.  If the user chooses cancel, I want to go back to the previous page.  I can do this using window.history.back().</p>
  
  <p>The problem is, if the user went directly to that page (app#settings) from another url (like google) by typing the url into the browser, I want to redirect the user to the home page (app/) rather than going back to google.</p>
  
  <p>I haven't been able to figure out any way to do this.  Backbone.history looks like it store information from the browser's back button, so it has a history even if they just arrived at the app.  I also couldn't find a way to view the previous url.</p>
  
  <p>Is this possible?</p>