add instance_accessor option to config_accessor

Changes:

* Add `instance_accessor` option to opt out of the instance writer and
  instance reader methods.
* Raises a NameError if the name of the attribute is not valid.
* Update documentation and tests.
* Add CHANGELOG entry in activesupport.

Resolver tests fail if mysql adapter not installed

One-liner code for logger in ActionView::Helpers::ControllerHelper

Accept a block in FormHelper#button

Fixed the Gemfile when gemspec is skipped in the 'rails plugin new' command

Metal controller doesn't have logger method, check it and then delegate

Fix #6591 Rails 3.2.5 Regression: incorrect _changed? for datetimes

being able to run the sqlite3 tests without that gem. This fix ensures
the tests will only run if the mysql gem is installed.

A better solution might be to move these tests into the per-adapter tests,
and test each adapter's resolver.

Updated guide to say Rails 4.0 requires 1.9.3 or higher, not Rails 3.2.

a test case that ensures AR::Relation#merge can merge associations

just a consolidation of the changelogs with minimal formatting

[ci skip]

This reverts commits 911a0859 and
30b31f51.

Reason: these changes make the Active Model tests fail randomly.

Some examples:
http://travis-ci.org/#!/rails/rails/jobs/1498992
http://travis-ci.org/#!/rails/rails/jobs/1496948
http://travis-ci.org/#!/rails/rails/jobs/1489985

This script was used to reproduce these breaks:
https://gist.github.com/f6828a03ee4d40bffbc3

200 times, 0 failures

Similarly to 65250022, this allows to use routes helpers for mounted
helpers, but this time in ActionView::TestCase

Correct the use of to_model in polymorphic routing

In integration tests, you might want to use helpers from engines that
you mounted in your application. It's not hard to add it by yourself,
but it's unneeded boilerplate. mounted_helpers are now included by
default. That means that given engine mounted like:

    mount Foo::Engine => "/foo", :as => "foo"

you will be able to use paths from this engine in tests this way:

    foo.root_path #=> "/foo"

(closes #6573)

remove unneeded blank line from !namespeced? generated controllers

Revert "Only include Rake::DSL if it's defined."

improve readability of AR explain result

modulize AR::NullRelation