Add tests to ActiveSupport:XmlMini to_tag method

[ci skip] Update code snippets to latest master (initialization.md).

Also update the `server.run` example (Replace Mongrel with Puma).

Correct factual error for page not found [ci skip]

Active support callback's before/after/around filters are not correctly making their singleton methods private

Make reflection and aggregate_reflection caches work with string keys.

cache.

with strings with string keys.

Related #14668.

add services: memcache to travis

The :source option for has_many => through should accept String values.

values.

With the changes introduced by 16b70fdd
it was expecting the value to be a Symbol, while it could be also a
String value.

Avoid URI parsing

This parsing is unecessary once the Request object already has the
needed information.

Add missing require so requiring `active_support/cache` works again.

Expand explanation of how to set secrets.yml.

Guides: minor typo fixed in Asset Pipeline guide

Fixed problem where `1.day.eql?(1.day)` is false

This fixes:
    1.second.eql?(1.second) #=> false

The new `eql?` requires that `other` is an `ActiveSupport::Duration`.
This requirement makes `ActiveSupport::Duration`'s behavior consistent
with other numeric types in Ruby.

    1.eql?(1.0) #=> false
    1.0.eql?(1) #=> false

    1.second.eql?(1) #=> false (was true)
    1.eql?(1.second) #=> false

    { 1 => "foo", 1.0 => "bar" }
    #=> { 1 => "foo", 1.0 => "bar" }

    { 1 => "foo", 1.second => "bar" }
    # now => { 1 => "foo", 1.second => "bar" }
    # was => { 1 => "bar" }

And though the behavior here hasn't changed, for reference:

    1 == 1.0 #=> true
    1.0 == 1 #=> true

    1 == 1.second #=> true
    1.second == 1 #=> true

Updates the maintenance policy with new Rails versions

Only apply DATABASE_URL for Rails.env

In passing, allow multi-word adapters to be referenced in a URL:
underscored_name must become hyphened-name.

The "DATABASE_URL_*" idea was moving in the wrong direction.

Instead, let's deprecate the situation where we end up using
ENV['DATABASE_URL'] at all: the Right Way is to explicitly include it in
database.yml with ERB.