Allow transparent upgrading of legacy signed cookies to encrypted cookies; Automatically configure cookie-based sessions to use the best cookie jar given the app's config

Added a regression test that will fail if anyone tries to change
time_zone_select to use grep again thinking it will work when it does
not.

A previous commit swapped out a call to select for a call to grep in
time_zone_options_for_select. This behavior actually causes the
regexp priority option to stop working.

ActiveSupport::TimeZone overrides the =~ operator which is what the
select block was using previously. Enumerable#grep
checks pattern === element and in this case that would be /US/ ===
ActiveSupport::TimeZone which does not work because
ActiveSupport::TimeZone does not supply an implicit converting to_str
method, only an explicit to_s method.

It would be impossible to provide a to_str method that behaves
identically to the =~ method provided on ActiveSupport::TimeZone
so the only option is to revert back to using select with =~.

When setting the layout either by referencing a method or supplying a
Proc there is no way to fall back to the default lookup behavior if
desired. This patch allows fallback to the layout lookup behavior when
returning nil from the proc or method.

* Fix named route collision in mount test fixture
* Update controller named route precedence test

Introduce UpgradeLegacySignedCookieJar to transparently upgrade existing signed cookies generated by Rails 3 to avoid invalidating them when upgrading to Rails 4

A recent change introduced the assumption that all controller actions
are known beforehand, which is not true when using action_missing.

If the host in `default_url_options` is accidentally set with a protocol such as 

```
host: "http://example.com"
``` 

then the generated url will have the protocol twice `http://http://example.com` which is not what the user intended. Likely they wanted to define a host `host: "example.com"` and a `protocol: "http://"` but did not know the convention.

This may not the most common problem, but when it happens it can go undetected for a while. I accidentally added `http://` out of habit recently only to find all the links in my emails were broken after deploying a demo site to production. Rather than allow this accident go undetected, we can fix the problem in line by properly setting the protocol and host.


I was able to find this related question on stack overflow: http://stackoverflow.com/questions/5878329/rails-3-devise-how-do-i-make-the-email-confirmation-links-use-secure-https-n where the answer was highly upvoted.

This is based off of work in #7415 cc/ @pixeltrix

ATP Action Mailer and Action Pack

The env hash passed to `Http::Headers#new` must be in env format.
Also be aware that the passed hash is modified directly.

docs and test-cases for setting headers/env in functional tests.

Follow up to #9700.

Handle conditional get in live requests - this will prevent error when using stale on live streams(issue #9636)

Closes #6513.

Also:
cleanup, use consistent syntax for `Http::Header` and test.

If an explicit name has been given and it already ends with "[]"

Before:

    select(:category, [], {}, multiple: true, name: "post[category][]")
    # => <select name="post[category][][]" ...>

After:

    select(:category, [], {}, multiple: true, name: "post[category][]")
    # => <select name="post[category][]" ...>

Fix ActionDispatch::Request#formats on xhr requests when HTTP_ACCEPT
header is empty string. About issue #7774, same fix as in commit bebb02fd
but for xhr requests.