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.

This feature enables the ability to load an
external routes file from the router via:
  draw :filename

External routes files go in +config/routes+. This
feature works in both engines and applications.

In the current router DSL, using the +match+ DSL
method will match all verbs for the path to the
specified endpoint.

In the vast majority of cases, people are
currently using +match+ when they actually mean
+get+. This introduces security implications.

This commit disallows calling +match+ without
an HTTP verb constraint by default. To explicitly
match all verbs, this commit also adds a
:via => :all option to +match+.

Closes #5964

It is in response for confusion in issue #5301

By default, resources routes are created with :resource/:id. A model
defining to_param can make prettier urls by using something more
readable than an integer ID, but since the route picks it up as :id you
wind up with awkward User.find_by_username(params[:id]) calls.

By overriding the key to be used in @request.params you can be more
obvious in your intent.

Allow the root route helper to accept just a string

There was a mix, sometimes patch first, sometimes put first.
Use always patch first, since this is going to be the
primary verb for updates.

uses PATCH for the forms of persisted records, and routes PATCH and PUT to the update action of resources

PATCH is the correct HTML verb to map to the #update action. The
semantics for PATCH allows for partial updates, whereas PUT requires a
complete replacement.

Changes:
* adds config.default_method_for_update you can set to :patch
* optionally use PATCH instead of PUT in resource routes and forms
* adds the #patch verb to routes to detect PATCH requests
* adds #patch? to Request
* changes documentation and comments to indicate support for PATCH

This change maintains complete backwards compatibility by keeping :put
as the default for config.default_method_for_update.

Too painful to lose the compact shorthand form!

This reverts commit e848c525.

Conflicts:

	actionpack/lib/action_dispatch/routing/mapper.rb

If you used dynamic constraint like that:

  scope :constraint => MyConstraint.new do
    mount RackApp => "/foo"
  end

routes were not displayed correctly when using `rake routes`.
This commit fixes it. If you want nice display of dynamic
constraints in `rake routes` output, please just override
to_s method in your constraint's class.

`path_names` can only be used for affecting `new` and `edit`

This reverts commit 3178cc9a.