Refactor `SchemaCreation#visit_AddColumn`
Fix a bug where AR::RecordNotSaved loses error messages

Since 3e30c5d, it started ignoring the given error message. This commit
changes the behavior of AR::RecordNotSaved#initialize so that it no
longer loses the given error message.
Refactor `add_column_options!`, to move the quoting of default value for :uuid in `quote_value`.
Rename to `quote_default_expression` from `quote_value`
docs, AR no longer makes use of `test:prepare`. [ci skip]

Change originated from https://github.com/rails/rails/pull/17739#issuecomment-64829088

/cc @metaskills
Merge pull request #17798 from kamipo/refactor_visit_add_column

Refactor `SchemaCreation#visit_AddColumn`
Removed ecosystem link from the header of the guides pages
Merge pull request #17809 from iainbeeston/remove_ecosystem_from_guides

Remove ecosystem link from guides
Merge pull request #17808 from yuki24/fix-bug-where-record-not-saved-loses-error-message

Fixed a bug where AR::RecordNotSaved loses the given error message
Adds preloaded_records method to NullPreloader

This fixes a regression where preloading association throws an
exception if one of the associations in the preloading hash doesn't
exist for one record.

Fixes #16070
4.2 release notes pass [skip ci]
Merge pull request #17811 from mrnugget/fixes_nested_association_preloading

Adds preloaded_records method to NullPreloader - fixes #16070
Merge pull request #17812 from jonatack/patch-8

4.2 release notes pass [skip ci]
Start Rails 5 development :tada:

We will support only Ruby >= 2.1.

But right now we don't accept pull requests with syntax changes to drop
support to Ruby 1.9.
We don't need to use sass-rails 5.0.0.beta
Use jquery-rails master to resolve dependencies

delayed_job_active_record doesn't allow Rails 5 yet
Merge pull request #17799 from kamipo/refactor_add_column_options

Refactor `add_column_options!`, to move the quoting of default value for :uuid in `quote_value`.
fixed indent of end in jdom.rb
Merge pull request #17818 from bigtone1284/edits_refactor_cop

fixed indent of end in jdom.rb
Prevent Numeric#to_s from allocating an array