cache_if(condition, option, &block) and cache_unless(condition, option, &block).

In the PR #8371 was introduced  conditional options :if and :unless in
the cache method.

    Example:

      <%= cache @model, if: some_condition(@model) do %>
        ...
      <%end%>

This is a good feature but *cache_if* and and *cache_unless*
are more concise and close to the standard of rails view helpers
(ex: link_to_if and link_to_unless).

    Example:

      <%= cache_if condition, @model do %>
      ...
      <%end%>

Related to the deprecation of Time.utc_time in favor of Time.utc,
in 48583f8b.

Fix rewinding in ActionDispatch::Request#raw_post

Conflicts:
	activerecord/test/cases/base_test.rb

If env['RAW_POST_DATA'] is nil, #raw_post will attempt to set it to
the result of #body (which will return env['rack.input'] if
env['RAW_POST_DATA'] is nil). #raw_post will then attempt to rewind
the result of another call to #body. Since env['RAW_POST_DATA'] has
already been set, the result of #body is not env['rack.input'] anymore.
This causes env['rack.input'] to never be rewound.

The Time.time_with_datetime_fallback, Time.utc_time and Time.local_time
methods were added to handle the limitations of Ruby's native Time
implementation. Those limitations no longer apply so we are deprecating
them in 4.0 and they will be removed in 4.1.

Both String and Date now respond to in_time_zone so we need to
check if the value is a Time or a DateTime.

Rely on the hub files for Time, Date and DateTime classes and
add the requires for String#to_time and String#in_time_zone.

This issue only happens on master due to internal AR refactorings, so
there is no need for a changelog entry.

The test was backported to 3-2-stable to ensure there won't be any regressions.

Explain how to supersede the new dynamic welcome page

The to_time_in_current_zone method doesn't match the naming of the methods
for converting to ActiveSupport::TimeWithZone on Time and DateTime. Since
DateTime inherits from Date that has led to confusion with some users
using the to_time_in_current_zone method with DateTime instances and having
the time part dropped and the UTC offset lost.

This commit fixes this by deprecating the old method and adding a new
in_time_zone method which matches the naming for DateTime and Time. This
should prevent accidently dropping times and UTC offsets when converting
DateTime instances to ActiveSupport::TimeWithZone.

The old, static welcome page instructed developers to delete the
public/index.html file and set a root route.  The new, dynamic welcome
page should tell developers (a) why they're seeing it when it doesn't
correspond to anything in the viewable app source and (b) that it can
be superseded with a root route.

This commit adds a convenience method for converting a string to an
ActiveSupport::TimeWithZone instance using the configured Time.zone or
another passed as an argument.

Match the controller and path names defensively.

Use '\A' instead of '^', and make the alteration shorter.

Use Rails to Render Default Index Page

attributes

This is an alternative implementation to #7771 thanks to the advice of @spastorino

Rails is a dynamic framework that serves a static index.html by default. One of my first questions ever on IRC was solved by simply deleting my public/index.html file. This file is a source of confusion when starting as it over-rides any set "root" in the routes yet it itself is not listed in the routes. By making the page dynamic by default we can eliminate this confusion.

This PR moves the static index page to an internal controller/route/view similar to `rails/info`. When someone starts a rails server, if no root is defined, this route will take over and the "dynamic" index page from rails/welcome_controller will be rendered. These routes are only added in development. If a developer defines a root in their routes, it automatically takes precedence over this route and will be rendered, with no deleting of files required. 

In addition to removing this source of confusion for new devs, we can now use Rails view helpers to build and render this page. While not the primary intent, the added value of "dogfooding" should not be under-estimated.

The prior PR #7771 had push-back since it introduced developer facing files. This PR solves all of the same problems, but does not have any new developer facing files (it actually removes one). 

cc/ @wsouto, @dickeyxxx, @tyre, @ryanb, @josevalim, @maxim, @subdigital, @steveklabnik

ATP Railties and Actionpack.

Conflicts:
	activerecord/CHANGELOG.md

This can be done using the class attribute cache_timestamp_format

Conflicts:
	railties/guides/source/configuring.textile

Conflicts:
	activerecord/test/models/bulb.rb
	activerecord/test/schema/schema.rb

Prevent raising EOFError on multipart GET request.

Such request can happen on Internet Explorer. When we redirect
after multipart form submission, the request type is changed
to GET, but Content-Type is preserved as multipart. GET request
cannot have multipart body and that caused Rails to fail.

It's similar fix to Rack's one:
https://github.com/chneukirchen/rack/blob/8025a4ae9477d1e6231344c2b7d795aa9b3717b6/lib/rack/request.rb#L224

the return value of mailer methods should not be relevant

Fix decorate_columns for finding only non-serialized columns

Use `File.expand_path` instead of `File.join`

database

fixtures