Fix grammar in Caching with Rails docs

Fix bug in ActionMailer guide.

When setting a mailer's default from address, you have to pass a hash
with a `:from` key; you can't pass just an email address.

Add support for Reply-To field in mail_to helper

Removed unused parameter to cookie serialize method

Describe full behaviour of Active Record's attribute query methods

Clarify that query methods have a custom definition of whether a numeric value is present. [ci skip]

The way Active Record query methods handle numeric values is a special case, and is not part of Rails's standard definition of present. This update attempts to make this more clear in the docs, so that people don't expect Object#present? to return false if used on a number that is zero.

References #18148.

Remove unneeded special case to calculate size for has_many :through

All cases are properly handled in CollectionAssociation
for all subclasses of this association

[ci skip]

We were ignoring the `default_value?` escape clause in the serialized
type, which caused the default value to always be treated as changed.

Fixes #18169

The code for `TableDefinition#references` and
`SchemaStatements#add_reference` were almost identical both
structurally, and in terms of domain knowledge. This removes that
duplication into a common class, using the `Table` API as the expected
interface of its collaborator.

This isn't Seattle.rb, @senny. ;)

Fix connection leak when a thread checks in additional connections.

Remove block from super

The code in `ConnectionPool#release` assumed that a single thread only
ever holds a single connection, and thus that releasing a connection
only requires the owning thread_id.

There is a trivial counterexample to this assumption: code that checks
out additional connections from the pool in the same thread. For
instance:

    connection_1 = ActiveRecord::Base.connection
    connection_2 = ActiveRecord::Base.connection_pool.checkout
    ActiveRecord::Base.connection_pool.checkin(connection_2)
    connection_3 = ActiveRecord::Base.connection

At this point, connection_1 has been removed from the
`@reserved_connections` hash, causing a NEW connection to be returned as
connection_3 and the loss of any tracking info on connection_1. As long
as the thread in this example lives, connection_1 will be inaccessible
and un-reapable. If this block of code runs more times than the size of
the connection pool in a single thread, every subsequent connection
attempt will timeout, as all of the available connections have been
leaked.

Reverts parts of 9e457a86 and
essentially all of 4367d2f0

Here you go, @senny. 😁

Add information about "allow_destroy" requiring an ID. [ci skip]

Conflicts:
	activerecord/CHANGELOG.md

I just wasted an absurd amount of time trying to figure out why my model
wasn't being deleted even though I was setting `_destroy` to true like
the instructions said. Making the documentation a little bit clear so
that someone like me doesn't waste their time in future.

Fixing numeric attrs when set to same negative value

fix typo in nodoc [ci skip]

Update Active Record's attribute query methods documentation to clarify that whether an attribute is present is based on Object#present?. This gives people a place to go see what the exact definition of presence is. [ci skip]

This bug occurs when an attribute of an ActiveRecord model is an
ActiveRecord::Type::Integer type or a ActiveRecord::Type::Decimal type (or any
other type that includes the ActiveRecord::Type::Numeric module. When the value
of the attribute is negative and is set to the same negative value, it is marked
as changed.

Take the following example of a Person model with the integer attribute age:

    class Person < ActiveRecord::Base
      # age          :integer(4)
    end

The following will produce the error:

    person = Person.new(age: -1)
    person.age = -1
    person.changes
    => { "age" => [-1, -1] }
    person.age_changed?
    => true

The problematic line is here:

    module ActiveRecord
      module Type
        module Numeric
          ...

          def non_numeric_string?(value)
            # 'wibble'.to_i will give zero, we want to make sure
            # that we aren't marking int zero to string zero as
            # changed.
            value.to_s !~ /\A\d+\.?\d*\z/
          end
        end
      end
    end

The regex match doesn't accept numbers with a leading '-'.

Describe gotcha for 'status' option [ci skip]

Update Active Record's attribute query methods documentation to describe its full behaviour. [ci skip]