Fix #10932. Treat "" and "::" as invalid on constantize

`initialize_on_precompile` is not used anymore.

recreate the models without mucking with internal caches of the relation
objects, then the test fails.

For example:

class Man < ActiveRecord::Base
  has_many :interests
end

class Interest < ActiveRecord::Base
  belongs_to :man
end

Then do this test:

def test_validate_presence_of_parent_fails_without_inverse_of
  repair_validations(Interest) do
    Interest.validates_presence_of(:man)
    assert_no_difference ['Man.count', 'Interest.count'] do
      man = Man.create(:name => 'John',
                       :interests_attributes => [{:topic=>'Cars'}, {:topic=>'Sports'}])
      assert_not_predicate man.errors[:"interests.man"], :empty?
    end
  end
end

The test will fail.  This is a bad test, so I am removing it.

We are setting this header to chrome=1 for Chrome Frame and this will be
retired soon. Check http://blog.chromium.org/2013/06/retiring-chrome-frame.html for
details

Conflicts:
	guides/source/upgrading_ruby_on_rails.md

This reverts commit 6df9c595.

This reverts commit 91a1cf70.

Reason: code changes disallowed in docrails, even if they are
guides generation related.

update format validation documetation

For example, you need to change this:

  class Author < ActiveRecord::Base
    has_many :posts
    has_many :taggings, :through => :posts
  end

  class Post < ActiveRecord::Base
    has_one :tagging
    has_many :taggings
  end

  class Tagging < ActiveRecord::Base
  end

To this:

  class Author < ActiveRecord::Base
    has_many :posts
    has_many :taggings, :through => :posts, :source => :tagging
  end

  class Post < ActiveRecord::Base
    has_one :tagging
    has_many :taggings
  end

  class Tagging < ActiveRecord::Base
  end

Push add column options to schema creation

Add `DateTime#usec` and `DateTime#nsec` so that `ActiveSupport::TimeWithZone`
keeps sub-second resolution when wrapping a `DateTime` value.

Fixes #10855

removed two instances of add_column_options! from abstract_mysql_adapter

reworked rename_column_sql to remove add_column_options from schema_statements

changed to use new hash syntax.

Refactor of ::Rails module

Use sprockets-rails 2.0.0

Drop extra variable from test