Menu blocks disappear when editing/saving in the Panels IPE

There's a couple things that will cause the Panels IPE to re-render a pane or the whole Panels display via AJAX:

1. Editing a particular pane will re-render that pane via AJAX
2. Saving will re-render the whole Panels display via AJAX

However, when rendering via AJAX, menu blocks will disappear. The reason they disappear is because they are figuring out the menu to display from the current path, and when rendering via AJAX, the current path is to the AJAX end-point -- not the original page.

When re-rendering a pane or a whole display via the Panels IPE, we should be minimally setting up Drupal's state to think it's at the original page so that menu blocks continue to render correctly.