Remove error setting when reading/deleting non-existent key.
Fixes #3813
Merge pull request #1265 from ADmad/master-cakesession-valid

Ensure session is not invalidated after reading/deleting non-existent key.
Fixed curly brackets at a few class definitions
Merge pull request #1267 from djbobke/coding-style-fixes

Small coding-style fixes
Make note of method removal.
Fix typo in link to cakephp book documentation
Merge pull request #1273 from mcreenan/master

Fix typo in link to cakephp book documentation
Avoid fail due to postgres ordering
Move App::uses() calls above the class.
Improve docblock for Object::log().
Update docs for Security::cipher()

This method is not cryptographically strong. Note that, and the
issues related to suhosin.

Related to #GH-1100
Fix test
Fix disabled attribute check.
Fixes #3818
Fix a problem of tag values which is not taken into account
(when equal to zero) when passing an XML object to an array.
Improve docs for AclShell.
Merge pull request #1276 from aymericderbois/2.3-XmlFixZeroValueProblem

Fix bug in Xml::_toArray Method
Prevent autoload when checking for the existence of HttpException

The class_exists check has been added in https://github.com/cakephp/cakephp/commit/4f29f58a5e9689adda104d77edf2c0cfe5101cd1#L1R28 to prevent a side effect with a PECL extension.

However if an autoloader such as the Composer one is loaded, it will try to require this `exceptions.php` file again:
```
    'HttpException' => $vendorDir . '/pear-pear.cakephp.org/CakePHP/Cake/Error/exceptions.php',
```
this will result in a "Fatal error:  Cannot redeclare class CakeBaseException"
Merge pull request #1277 from real34/patch-1

Prevent autoload when checking for the existence of HttpException
Split sentence into two sentences
Merge pull request #1279 from cakebaker/patch-1

Split sentence into two sentences
Make named capture groups compatible with older PCRE versions.

CentOS is terrible and generally contains very old versions of PCRE.
Update patterns to use more backwards compatible named capture groups.

Fixes #3821