Tests are failing due to missing env var on master https://travis-ci.org/rails/rails/jobs/15930622#L641

This adds an environment variable `ENV['RAILS_SECRET_KEY_BASE']` so these tests will pass.

[ci skip] Update getting started Ruby version.

Do not store production information in .yml files

Missed AMo when adding to the other components in
ae196e85.

This commit also cleans up the rake tasks that were checking
for DATABASE_URL in different places.

In fact, it would be nice to deprecate DATABASE_URL usage in the long
term, considering the direction we are moving of allowing those in .yml
files.

Always pass in the column for quote_bound_value and quote using it in
case it exists there.

Fixes #12261. Closes #12395.

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/test/cases/adapters/postgresql/array_test.rb
	activerecord/test/cases/adapters/postgresql/json_test.rb

The code uses these checks in several places to know what to do with a
particular column, for instance AR attribute query methods has a branch
like this:

    if column.number?
      !value.zero?
    end

This should never be true for array columns, since it would be the same
as running [].zero?, which results in a NoMethodError exception.

Fixing this by ensuring that array columns in PostgreSQL never return
true for number?/text? checks.

Since most of the array support was based on the postgres_ext lib, it's
worth noting it does the same thing for numeric array columns too:

https://github.com/dockyard/postgres_ext/blob/v1.0.0/lib/postgres_ext/active_record/connection_adapters/postgres_adapter.rb#L72

This extended the same logic for text columns to ensure consistency.

TLDR: always return an object that responds to the query methods from
request.format, and do not touch Mime::Type[] lookup to avoid bugs.

---

Long version:

The initial issue was about being able to do checks like
request.format.html? for request with an unknown format, where
request.format would be nil.

This is where the issue came from at first in #7837 and #8085
(merged in cba05887), but the
implementation went down the path of adding this to the mime type
lookup logic.

This unfortunately introduced subtle bugs, for instance in the merged
commit a test related to send_file had to be changed to accomodate the
introduction of the NullType.

Later another bug was found in #13064, related to the content-type being
shown as #<Mime::NullType:...> for templates with localized extensions
but no format included. This one was fixed in #13133, merged in
43962d6e.

Besides that, custom handlers were not receiving the proper template
formats anymore when passing through the rendering process, because of
the NullType addition. That was found while migrating an application
from 3.2 to 4.0 that uses the Markerb gem (a custom handler that
generates both text and html emails from a markdown template).

---

This changes the implementation moving away from returning this null
object from the mime lookup, and still fixes the initial issue where
request.format.zomg? would raise an exception for unknown formats due to
request.format being nil.

[ci skip] a destroy action in controller, not delete [getting_stated.md].

Instead, read information from environment variables.

Tell how to Create a Database in Error Message

Currently if you attempt to use a database that does not exist  you get an error:

```
PG::ConnectionBad FATAL:  database "db_error" does not exist
```

The solution is easy, create and migrate your database however new developers may not know these commands by memory. Instead of requiring the developer to search for a solution, tell them how to fix the problem in the error message:

```
ActiveRecord::NoDatabase: FATAL:  database "db_error" does not exist
Run `$ bin/rake db:create db:migrate` to create your database
```

Active Record should not know about `rake db:migrate` so this additional information needs to come from the railtie. Potential alternative implementation suggestions are welcome.

On destroying do not touch destroyed belongs to association.

Fixes: #13445

Resolver test cases

Add missing av/railtie require

Fix typecasting array of integers

Closes #13444

Fix DB Console tests

The build is broken: https://travis-ci.org/rails/rails/builds/15824530

This commit fixes it.

The problem: Sqlite expects the `database` part to be an absolute path. That prompted this change to be committed to master: https://github.com/rails/rails/commit/fbb79b517f3127ba620fedd01849f9628b78d6ce

This change provides correct behavior. Unfortunately tests were introduced in https://github.com/rails/rails/commit/971d5107cd4cd08c22a85d34546f4ba03ed5c925 that were relying on the incorrect behavior. We can avoid the fix by changing to another database url such as `mysql` or `postgresql`

In addition to fixing the failure, the assertions are changed so that the "expected" value comes before "actual" value.

Enable memcached service on travis for running cache tests.