Fixed custom validation context bug for child associations

Use #include? instead of #any?, make it simpler

Test typecasting on instance rather than class itself

Also change other related test to use existing record rather than
creating new one.

bind parameters we not being propogated to simple subquery calculation
calls. This fixes it

Add singular and plural form for some validation messages

[ci skip] Update guides license to CC BY-SA 4.0 International.

Plugin gemspec

Benefits: https://creativecommons.org/version4

This commit adds new lines between titles, paragraphs and code blocks
for an easier reading.

Moreover, in order to be consistent with the other guides, let's remove
the sharps on the right side of the different titles.

The "Running a Single Test" part was also explained after the "Testing
Active Record" one which shows how to run a single test under the scope
of a specific adapter.

Finally, let's explain the `-n` option to run a specific test method.

Form_tag_helper grammar fix [skip ci]

I think this is wrong, but it gets the build passing for now. We should
always add options, but we need to make more guarantees about how the
underlying url helper is called

if you want options, don't mix them with the first hash, just pass them
all in with the second hash

Symbolize variables of mysql/mysql2 connection configuration

Conflicts:
	activerecord/CHANGELOG.md

always use File.join in asset_path

[ci skip] Security guide clarity.

Update mapper.rb

Make remote_ip detection properly handle private IPv6 addresses

Conflicts:
	actionpack/CHANGELOG.md

SQLite3: Always close statements.

Conflicts:
	activerecord/CHANGELOG.md

Avoid unnecessary conditional block

GeneratedAttribute#column_name checks already for reference? on the
attribute returning the right name to use as symbol for label and field.