Conflicts:
	guides/source/4_1_release_notes.md

We need to fix this test

added missing require to active_support/tagged_logging

we’re using .delegate and should require it.

This behavior is documented in our guides (http://edgeguides.rubyonrails.org/action_mailer_basics.html#action-mailer-callbacks)
but was broken in the past. This commit short curcuits
the `mail` method if:

  1. mail() was previously called
  2. no headers are passed
  3. no block is passed

Closes #13090.

/cc @pixeltrix

Typo and grammatical fixes [ci skip]

Fix `rake test` description in the guides [ci skip]

Missing partial folder/_partial instead of folder/partial.

Closes #13002.

Move Rack::Cache after ActionDispatch::Static in the middleware stack

he or she => they

A path redirect may contain any and all parts of a url which have different
escaping rules for each part. This commit tries to escape each part correctly
by splitting the string into three chunks - path (which may also include a host),
query and fragment; then it applies the correct escape pattern to each part.

Whilst using `URI.parse` would be better, unfortunately the possible presence
of %{name} parameters in the path redirect string prevents us from using it so
we have to use a regular expression instead.

Fixes #13110.

Removing some gender sensitive object pronouns

Use gender - neutral pronouns in security guide.

related  #49ff20d9

Use .railsrc while creating new plugin if available. Fixes #10700

- Fixes #10700

JSON encoder internals showed up in docs [ci skip]

AS::TimeZone's cache thread safety

Removed redundant field name in the guide

Fixes: #13108
[ci skip]

Update render with a spacer_template [ci skip]

Fix segmentation fault in Ruby 2.0.0-p353.

Typo fixes [ci skip]

In Ruby 2.0.0-p353 there was a
[commit](https://github.com/ruby/ruby/commit/66915c507777c5e3a978fa73de25db763efd9206)
that switched case matching from actual sending `===` method to magic lookup,
that does not see it in `method_missing`. It's hard to predict how exactly and
when exactly this bug will be solved so here I suggest a solution of defining
it in Duration directly.

In Ruby 2.0.0-p353 without the added fix added test crashes to segmentation
fault.

[ci skip]

Raise `ArgumentError` when `has_one` is used with `counter_cache`

Previously, the `has_one` macro incorrectly accepts the `counter_cache` option
due to a bug, although that options was never supported nor functional on
`has_one` and `has_one ... through` relationships. It now correctly raises an
`ArgumentError` when passed that option.

For reference, this bug was introduced in 52f8e4b9.