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`
Remove $VERBOSE = nil from tasks.rb

Permanently setting $VERBOSE to nil causes unwanted side effects (warnings generated by app code are
silenced when triggered by a rake task but visible otherwise). silence_warnings {} would be safer to
use here since it resets $VERBOSE back to what it was when the block finishes.
Refactor `ArrayParser`

* Constantize parse token
* Remove extra param passed to `parse_data`
grab executable from rubygems

As done here d7fc97d3f90c0e30865d32ce202658f03248cacc
Update of 'The Asset Pipeline' guide for Rails 4. [ci skip]
Changed stylesheet load order in the stylesheet manifest generator.
Merge pull request #11640 from pawel2105/manifest_fix

Changed stylesheet load order in the stylesheet manifest generator.
Don't rewrite AR connection#commit_db_transaction method globally
Unneeded assertion
Clear class ivar before testing
Properly repair validations when dynamically added
Revert "fix order dependent test related to migration"

This reverts commit 10259c3e906da2191ef0d43cd664a3b5504d9f8c.

reason: this causes rake test_mysql and test_mysql2 fail
Avoid "uninitialized constant ActiveRecord::PendingMigrationError::Rails"
Add ability to specify how a class is converted to Arel predicate

This adds the ability for rails apps or gems to have granular control
over how a domain object is converted to sql. One simple use case would
be to add support for Regexp. Another simple case would be something
like the following:

    class DateRange < Struct.new(:start, :end)
      def include?(date)
        (start..end).cover?(date)
      end
    end

    class DateRangePredicate
      def call(attribute, range)
        attribute.in(range.start..range.end)
      end
    end

    ActiveRecord::PredicateBuilder.register_handler(DateRange,
      DateRangePredicate.new)

More complex cases might include taking a currency object and converting
it from EUR to USD before performing the query.

By moving the existing handlers to this format, we were also able to
nicely refactor a rather nasty method in PredicateBuilder.
Added Time#middle_of_day

Added middle_of_day method to Date and DateTime
Merge pull request #11608 from arunagw/ruby-from-rubygems

grab executable from rubygems
Add Time#to_s(:iso8601) for easy conversion of times to the iso8601 format for easy Javascript date parsing
remove duplicate method

This method is already present in helper.rb
use method with_active_record_default_timezone