Improve the testing guide [ci skip]

Improve the "Testing Rails Applications" guide adding a section for
testing helpers and a little note about associations with ActiveRecord
and YAML fixtures.

Also add a link to Fixture Builder ; yet another replacement for
fixtures such as Machinist or FactoryGirl.
Remove conditional, since results are always an instance of `ActiveRecord::Result`
Added SanitizeHelper to rails guide docs [ci skip]

Added SanitizeHelper to rails guide docs [ci skip]

Added SanitizeHelper to rails guide docs update [ci skip]
Creating an SSE class to be used with ActionController::Live.
Rails.logger should have level specified by config.log_level. 

Fix bug when log level of Rails.logger (which was set via config.logger) does not match the    config.log_level.
fix tests
update guide to reflect default HMAC SHA1 in MessageVerifier used in SignedCookieStore [ci skip]
remove language about configuring digest method [ci skip]
Minor optimization and code cleanup in query_methods.

- Use symbols rather than strings where possible to avoid extra object construction
- Use destructive methods where possible to avoid extra object construction
- Use array union rather than concat followed by uniq
- Use shorthand block syntax where possible
- Use consistent multiline block styles, method names, method parenteses style, and spacing
Fix ActiveSupport::Testing::Isolation on jruby

Hopefully the first of many related to #11700.

With these changes the railties tests wont 100% pass but at least they
will run and show the errors.

The first problem was the @method_name variable was never set.
This was causing ENV["ISOLATION_TEST"] to always be nil which
would cause the test output to never be written to the tempfile.

The second problem was that an invalid -t option was being passed
to minitest and minitest was erroring out.

The third problem was the run method needs to always return an
instance of the test class it is trying to isolate. We were returning
a ProxyTestResult instead.
Replaced quotation marks for term by apostrophe

in getting started guide for section 5.6

[ci skip]
Define enable_extension method to prevent undefined method error

When mixing postgresql and another adapter like sqlite3 (for dev and test
respectively), the task `db:test:prepare` will fail due to the `enable_extension`
method not being defined in the abstract adapter. This patch simply adds an
empty definition to prevent it.
Merge pull request #11455 from antonio/fix_enable_extension_not_being_defined

Define enable_extension method to prevent undefined method error
Added action_view in Rails::Info
Merge pull request #11720 from arunagw/added-av-in-rails-info

Added action_view in Rails::Info
Add timeout to test_async_stream

Without timeout:
this test executed infinitely on JRuby
Passes on MRI

With Timeout:
this test gracefully fails on JRuby
Passes on MRI, tested on v2.0 & v1.9.3
Added Action View in 'rake about' [ci skip]
Merge pull request #11716 from jetthoughts/use_backquote_for_terms_in_getting_strated

Replaced quotation marks for term by apostrophes in getting started guide [ci skip]
As we are doing debug mode on

we don't need to silenced it
Merge pull request #11722 from arunagw/removed-deprecation-silenced-from-test

As we are doing debug mode on