Be able to use 'reverse' direction, even if you disable back-button handlers (for example when using jqm with backbone.js)

## Context: 
- jQuery Mobile + backbone.js App.
- jQuery Mobile bindings/history/routing were disabled to use Backbone's.
- Back buttons are being used manually (that means using window.history.back directly)

## Problem: 
- 1.1.1 won't apply the reverse direction even if you set the link with data-direction="reverse" to the links.

## Example:

For example having:
(based on <http://coenraets.org/blog/2012/03/using-backbone-js-with-jquery-mobile/> )

```
  # Disable jQuery Mobile routing and history to use Backbone.
  $.mobile.ajaxEnabled = false
  $.mobile.linkBindingEnabled = false
  $.mobile.hashListeningEnabled = false
  $.mobile.pushStateEnabled = false

  # Enable back buttons by default
  $.mobile.page.prototype.options.addBackBtn = true
```

This will add the back button, but since all the handlers are disabled, you need to redirect to the last page manually:

```
($('a[data-rel="back"]')).live('click', function() {
  window.history.back();
});
```

That will work. But sadly you won't see the default reverse direction for any back button. But it will be fixed by setting the ` $.mobile.forceReverse = true`. So letting the application to use forward direction by default, and reverse for all the back buttons.

```
($('a[data-rel="back"]')).live('click', function() {
  $.mobile.forceReverse = true;
  window.history.back();
});
```

That change won't affect any other place than the Back buttons. And the variable is `false` by default.
I've included the Documentation changes too.