Use the master request from the stack

I think this solves #84, though not sure if it will cause problems with ESI.  Can anyone confirm?

Always using the master request from the request stack means that we're only concerned about the locale of the controlling page.

why does this fix the locales array being empty? would this not only be able to fix things related to losing the locale?

and would it not be enough to ensure the subrequest carries the correct locale?