Updated the preformance_testing guide to reflect the fact that prof-rails no longer needs to be fetched from github

Add `#environment`

Update function signatures for `#gem` and `#generate`.

Fixes #2468.

It's actually the FileStore.

Fixes #8130.

The shortcut ampersand syntax of `select.map(&:field)` is same thing as `.plunk(:field)`. document that

This reverts commit 223ed2b4.

Reverting since rake routes right align named route. See some discussion in
https://github.com/lifo/docrails/commit/223ed2b4832d63853b61ccb8e9ff82fcd835e61f#commitcomment-2104595

Conflicts:
	actionpack/lib/action_controller/metal/mime_responds.rb
	activerecord/lib/active_record/attribute_methods.rb
	guides/source/working_with_javascript_in_rails.md

This reverts commit 3b890520.

Reason: changes made to a test, albeit in commented lines - non-uniform
change.

[ci skip]

This reverts commit cd17ee55.

Reason: Let's note that this is discouraged, not remove the docs

[ci skip]

This reverts commit f4ad0ebe, reversing
changes made to 8b2cbb3a.

Conflicts:
	actionpack/CHANGELOG.md

REASON: This added introduced a bug when you have a shorthand route
inside a nested namespace.

See
https://github.com/rafaelfranca/rails/commit/281367eb770faf8077c1fd6194188e92ed1637a1

Fixed mapping of Solomon Islands.

Fixes #8095.

For reference, here is the discussion about the mapping being
incorrect:
http://rubyforge.org/pipermail/tzinfo-users/2012-November/000114.html

memoize calculated ip without additional variable

There is no need in additional `@calculated_ip` instance variable.

When calling first(n) or last(n) in a collection, Active Record was
improperly trying to set the inverse of instance in case that option
existed. This change was introduced by
fdf4eae5.

In such cases we don't need to do that "manually", since the way
collection will be loaded will already handle that, so we just skip
setting the inverse association when any argument is given to
first(n)/last(n).

The test included ensures that these scenarios will have the inverse of
instance set properly.

Fixes #8087, Closes #8094.

Squashed cherry-pick from d37d40b2 and c368b660.

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/lib/active_record/associations/collection_association.rb