Fix a couple of Ajax related path issues

  - Include context path when generating page specific JS
  - Include context path when making Ajax requests
  - Fix Ajax path matching (previously renderVersion was being set to
    "ajax")

fixes #1591 
The specific situation that I needed it was to provide a way for a non-Lift Ajax request (made by a third party JS component) to grab page (RequestVar) context.

The alternative would be duplicating the code from lift.js that grabs this from the DOM (at the cost of breakage as this evolves).