Action caching ignores format for XMLHttpRequest

If there is no format specified in url, a chosen template differs for XMLHttpRequest (js is used)
and non-XMLHttpRequest (html is used). Cache fragment name is the same for both request types.

If the cache fragment is created by normal (non-XMLHttpRequest) request with no format specifier
(i.e. /books) and than the same page is accessed via XMLHttpRequest, a cached fragment in html format will be returned and the page would be probably broken. The same problem happens when the
fragment is created by XMLHttpRequest and than the page is accessed via non-XMLHttpRequest.

This code:

class BooksController < ApplicationController
  caches_action :index
  ...

views/myserver/books.cache

I think fragment should have extension according to template which was used:

views/myserver/books.html.cache
views/myserver/books.js.cache

I found this bug in Rails 2.2.2., Rails 2.3.3. and the Edge Rails. A patch for Edge Rails is attached.