fix the sql that is generated from scoping
Bring config.allow_concurrency back

Since the Rack::Lock still exists in development,
let's provide a way to disable it explicitly.
Created an unscope method for removing relations from a chain of
relations. Specific where values can be unscoped, and the unscope method
still works when relations are merged or combined.
Merge pull request #9532 from neerajdotname/fix-sql-in-example

In example fix sql that is generated from scoping
Merge pull request #9200 from wangjohn/unscoping_activerecord_merging

Introduce relation #unscope
add prompt to 422 page to check logs
Merge pull request #9537 from NARKOZ/patch-6

add prompt to 422 page to check logs
Use 1.9 hash style in changelog and doc examples [ci skip]
Remove .all usage from unscope doc examples [ci skip]
Fix formats on xhr requests when HTTP_ACCEPT is empty string

Fix ActionDispatch::Request#formats on xhr requests when HTTP_ACCEPT
header is empty string. About issue #7774, same fix as in commit bebb02f
but for xhr requests.
Fixed typo in active record's changelog
Merge pull request #9540 from dimko/patch-1

Fixed typo in active record's changelog
Merge pull request #9541 from maximerety/fix_7774

Fix formats on xhr requests when HTTP_ACCEPT is empty string
only calculate next_id when we need a new method defined
rewrite tests to have no side-effects on `include_root_in_json`.
`ActiveRecord::Base.include_root_in_json` is `false` by default.

Closes #9459.

The PR #6597 unified the configuration for `include_root_in_json`
in AM and AR to `false`.
Later on with the refactoring commit: e030f26 the value in AR was
set to `true` but I think this was not on purpose.

With this commit both AM and AR will have the same configuration
for `include_root_in_json`, which is `false`.
Merge pull request #9467 from senny/9459_include_json_root_out_of_sync

`ActiveRecord::Base.include_root_in_json` is `false` by default.
adds guides/.document to tell rdoc not to process this directory

When the Rails 4 gem is installed rdoc sees markdown files below the
guides directory and processes them. With an empty .document file
we prevent that from happening. Thanks to @drbrain for the tip.