Fix a race condition problem

Prevents Model::save() from generating a query with WHERE 1 = 1 on race condition.

Refs #3857
Fix CS
Merge pull request #3959 from chinpei215/master-issue3857-fix

Fix a race condition problem

Fixes #3857
Update CONTRIBUTING.md

Added some helpful links. Updated PHPUnit version requirement.
Merge pull request #3976 from davidyell/patch-2

Update CONTRIBUTING.md
Make the error message better for fixture errors

The stack trace has no details about which fixture is the actual problem.
Merge pull request #3985 from dogmatic69/patch-3

Make the error message better for fixture errors
Make SMTP auth reply code checks work properly.
Add some more exception message checks
When specifying Session as a component and using Session flash messages, you end up with 'Paginator, Session, Session' which doesn't make sense. Added an array_unique to remove any duplicated components.
Merge pull request #4008 from davidyell/patch-3

Update ControllerTask.php
Added *.mo and .idea to .gitignore
Merge pull request #4016 from ravage84/patch-1

Added *.mo and .idea to .gitignore
Add `.` to the list of allowed characters.

This was missed when the email validation rules were relaxed in
dc34d80f6f622e883b8c7db9ef489bd514c8701f.

Fixes #4027
Update version number to 2.5.3
Added NetBeans project folder to .gitignore

Refs https://github.com/cakephp/cakephp/commit/78fb9b559ab1745a7255583231694be99cec65c5#commitcomment-7077015
Update db_acl.sql to use correct column names.

The column names added in bb15271 were incorrect.

Fixes #4052
Add indexes to db_acl.sql in skel directory.

Copy changes in app/Config/Schema into the skel directory.

Refs #4052
Fixed sending of headers when ajaxLogin is set
Added test case for CakeResponse::send() and ajaxLogin