Fix AC::TemplateAssertions instance variables not resetting.

Fixes https://github.com/rails/rails/issues/16119.
Fixes #16255 [ci skip]
Merge pull request #16256 from akshay-vishnoi/doc-change

Fixes #16255 [ci skip]
Merge pull request #16234 from tgxworld/fix_template_assertion_for_integration_test

Fix AC::TemplateAssertions instance variables not resetting.
`create` return an active record object with erros instead of false when validation fails. [skip ci]
Merge pull request #16237 from tonytonyjan/patch

`create` method returns an active record object with errors instead of false when validation fails. [skip ci]
specify N=0 to prevent parallel tests (just run tests on the main process)
Use PROCESS_COUNT to define the number of parallel executors
Split Action Pack tests in a new job on travis

This will make easier to compare run time between Ruby 2.1 and trunk
Set Psych as the YAML engine for Rubinius

Since the rubysl-yaml gem doesn't ship with Psych by default because of
its dependency on libyaml, on Rubinius, the default engine is Syck.

However, if we want to be able to run the application safely on
different rubies, we need to make people using Rubinius rely on Psych.

See http://git.io/uuLVag for further information.
Do not set enforce_available_locales to i18n 0.7

Now the default is always true.

Users still can set it using config.i18n.enforce_available_locales.
Merge pull request #16267 from robin850/rbx-yaml

Set Psych as the YAML engine for Rubinius
Dev and edge application and plugins need to include i18n master
Fix syntax error
Remove mocha usage
Calling require_self twice in css raises Sprockets::ArgumentError exception [ci skip]
Merge pull request #16260 from akshay-vishnoi/doc-change

Calling require_self twice in css raises Sprockets::ArgumentError exception [ci skip]
[ci skip]Add i18n master to the Gemfile
Merge pull request #16276 from y-yagi/bug_report_templates

[ci skip]Add i18n master to the Gemfile
pg, `change_column_default, :table, :column, nil` issues `DROP DEFAULT`.

Closes #16261.

[Matthew Draper, Yves Senn]

Using `DEFAULT NULL` results in the same behavior as `DROP DEFAULT`.
However, PostgreSQL will cast the default to the columns type,
which leaves us with a default like "default NULL::character varying".

/cc @matthewd