3.0 - Fix issue where conditions that are valid global methods get treated as callables

I encountered an issue where certain query conditions where being treated as a callable by Cake\Database\Expression\QueryExpression.

A simple example:
```
$query = $Table->find('all')
->where([
    'my_field' => 'h'
]);
```

would throw

```
Warning Error: htmlspecialchars() expects parameter 4 to be boolean, object given in [vendor\cakephp\cakephp\src\basics.php, line 255]                                                    
                                                                                                                                                                                             
2014-07-22 07:56:10 Warning: Warning (2): htmlspecialchars() expects parameter 4 to be boolean, object given in [vendor\cakephp\cakephp\src\basics.php, line 255]                         
Trace:                                                                                                                                                                                       
Cake\Error\BaseErrorHandler::handleError() - ROOTvendor\cakephp\cakephp\src\Error\BaseErrorHandler.php, line 135                                                                             
htmlspecialchars - [internal], line ??                                                                                                                                                       
h - ROOTvendor\cakephp\cakephp\src\basics.php, line 255                                                                                                                                      
Cake\Database\Expression\QueryExpression::_addConditions() - ROOTvendor\cakephp\cakephp\src\Database\Expression\QueryExpression.php, line 440                                                
Cake\Database\Expression\QueryExpression::add() - ROOTvendor\cakephp\cakephp\src\Database\Expression\QueryExpression.php, line 121                                                           
Cake\Database\Query::_conjugate() - ROOTvendor\cakephp\cakephp\src\Database\Query.php, line 1565                                                                                             
Cake\Database\Query::where() - ROOTvendor\cakephp\cakephp\src\Database\Query.php, line 735                                                                                        
```

I'm unsure if this may adversely affect other components or use-cases?