Fix doc in Postgres database creation
add active model basics wip to guides/documents.yaml
support :unless_exist for FileCache
Merge pull request #11564 from zzak/active_model_guide

[Guides] Active Model Basics [ci skip]
use a queue rather than a list. fixes #12069
Merge pull request #11785 from grosser/grosser/file-unless-exist

support :unless_exist for FileCache

Conflicts:
	activesupport/CHANGELOG.md
	activesupport/test/caching_test.rb
always call set_default_accessors from create_root
fix template Gemfiles
Remove confusing generated-code commentary
Add failing test for preloading with a polymorphic association and using the existential predicate
Fix broken delete_all test, which will now be failing since #delete_all is broken
Merge pull request #10664 from aderyabin/docpatch

Fix doc in Postgres database creation [ci skip]
Revert "add active model basics wip to guides/documents.yaml"

Reason: WIP guides are not in the index because they are partial
work pushed to the repo. Either there is someone working on them
or else the work was interrupted.

Guides are added to the index page when they are finished, the
author considers the draft to be complete, someone reviews them,
and overall they are considered to be good for users to read.

This reverts commit eefc03a8069bddfe31751c4bd4fb1804e7f33c2c.
Update testing.rake with more accurate description of test task.

According to #5ecd12 change.

[ci skip]
Merge pull request #12688 from simi/patch-1

Update testing.rake with more accurate description of test task.
Clarify that visiting http://localhost:3000 should be done in a browser.
Merge pull request #12690 from durrantm/minor_README_change

Clarify that visiting http://localhost:3000 should be done in a browser. [ci skip]