Serialize the `last_request_at` entry as an Integer

Pushing the `Time` object inside the session has inconsistencies
across different serializers and we should use a more primitive type
so we don't need any specific parsing logic for the JSON serializer.
Use _url routes instead of _path
Merge pull request #2954 from plataformatec/lm-last-request-at-json-serialization

Serialize the `last_request_at` entry as an Integer
Remove need for raw session inspect
Update CHANGELOG
Use scope instead of constraints to define routes.
It works the same with rails 3 and rails 4.
Merge pull request #2960 from kgiszczak/redirect-url-tweaks

Use full urls instead of just paths when redirecting in failure app.
Add the invalidate_all_sessions_on_logout configuration to invalidate
all the remember me tokens when the user signs out.
Merge pull request #2964 from plataformatec/invalidate_all_sessions_on_logout

Add configuration to invalidate all the remember me tokens when the user signs out.
Use port option in default url options for ActionMailer
Cache bundle results on Travis to S3
Merge pull request #2965 from sadjow/use-port-option-on-default-url-options

Use port option in default url options for ActionMailer
Check if there is a signed in user before sign out.

Only execute the `SessionsController#destroy` if there is a signed in
user, otherwise it will raise
`ActionController::InvalidAuthenticityToken`.

Fixes #2934.
Merge pull request #2968 from plataformatec/sign_out_not_logged_in_user

Check if there is a logged user before logout.
Merge pull request #2955 from lucasmazza/lm-cached-bundle

Cache bundle results on Travis to S3
Update Travis encrypted keys
support multiple warden configuration blocks

Changes the behavior of `Devise.warden` such that calling it multiple
times with different blocks will result in a call to each block on
`Devise.configure_warden!` rather than "last block wins". This is
especially used for plugins that wish to extend warden functionality
without clobbering base app configuration or vice versa.
Merge pull request #2978 from rossta/support_for_multiple_warden_config_blocks

Support multiple warden configuration blocks
Add CHANGELOG entry for #2978 [ci skip]