Don't require 'turn' from rails/test_help

If 'turn' is in the Gemfile with `:require => nil`, Rails should
respect that.

This supports the case where 'turn' may or may not be required
depending on different developers' preference or environment. E.g., you
require turn for local testing, but not on your CI server by putting
this in `test/test_helper.rb`:

    require 'turn' if ENV['TURN']
Update guides/source/getting_started.md

Reflect change in 009873a that renamed the script/ folder to bin/
improve StrongParameters documentation [ci skip]
Merge pull request #8803 from frodsan/sp_docs

Improve StrongParameters documentation [ci skip]
Fix named scope + class method example

Closes #8804 [ci skip]
let the rails gem ship with the README

The doc:rails application rake task needs this README.
doc/README_FOR_APP is no longer generated
new README generated for new apps
Reset AR::Migration.verbose change to avoid depending on test run order
Reset test data, and fix bug that the inserted data were not actually selected
Fix readme tests

Related to the change introduced in 6cf47c533d7d6784d34fc31406a335555e0c32b8.
Initialize instance variable to remove warning

    actions.rb:34: warning: instance variable @in_group not initialized
Merge pull request #8802 from claudiob/patch-1

Update guides/source/getting_started.md [ci skip]
Avoid Rack security warning no secret provided

This avoids "SECURITY WARNING: No secret option provided to Rack::Session::Cookie."
Merge pull request #8801 from ktheory/dont_require_turn

Don't require 'turn' from rails/test_help
Don't configure Turn output, we aren't using it since 3.2.0
change unless !blank? to if blank? in get_primary_key
Use absolute path

It is semantically correct than relative path.
Merge pull request #8808 from tricknotes/use-absolute-path

Use absolute path [ci skip]
Merge pull request #8800 from acapilleri/primary_key

refactor reset_primary_key and change !blank? to present? in get_primary...