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 
Heh wait, this isn't actually doing what it appears to be doing. If we want to check that it's actually the same value as `liftPath`, we need to do:

```scala
  case `liftPath` :: "ajax" ...
```