Raise a rescuable exception when Rails doesn't know what to do with the format, rather than responding with a head :not_acceptable (406)

SessionStore was recently changed to delegate to hash
object instead of inherit from it. Since we don't want
to extend SessionStore with every method implemented in
Hash, it's better to just convert any object passed to
debug_hash (which is also better as we don't require
to pass Hash instance there, it can be any object that
can be converted to Hash).

specify a role for identifying accessible attributes when wrapping params

This fixes the following scenario:

    resources :contacts do
      post 'new', action: 'new', on: :collection, as: :new
    end

Where the /new path is not generated because it's considered a canonical
action, part of the normal resource actions:

    new_contacts POST   /contacts(.:format)          contacts#new

Fixes #2999

If a user gets a routing error due to a view helper such as using user_path without an :id they must go to their logs to see the backtrace. By adding in the trace template, a user can see which line the error occurred on without leaving the browser.

When a routing error occurs outside of the view the application trace will be blank and will not confuse developers.

A callable object passed as a constraint for a route may access the request
parameters as part of its check. This causes the combined parameters hash
to be cached in the environment hash. If the constraint fails then any subsequent
access of the request parameters will be against that stale hash.

To fix this we delete the cache after every call to `matches?`. This may have a
negative performance impact if the contraint wraps a large number of routes as the
parameters hash is built by merging GET, POST and path parameters.

Fixes #2510.