Ticket #8614: Default page cache path to the current request path

Currently, cache_page regenerates the cached path from the current
params (controller, action, etc). By default, page should be cached at
the path they are requested for (doesn't that only make sense?).

Example
  map.root :controller => "welcome"
  GET /

Caches output to "public/welcome/index.html" when we want it to be at
"public/index.html".

http://dev.rubyonrails.org/ticket/8614

Applied.