Postgres buildColumn() support for array-type columns.

It is now possible to write unit test fixtures that create
tables featuring array-type columns. If your database happens
to have advanced data types with custom names, those should
be fine, too (ex: tic_tac_toe[3][3] representing X's and O's).
The core idea was to support any of the basic types being
postfixed with the array-type notation.

An example fixture:

```
class RatingFixture extends CakeTestFixture {
  public $table = 'ratings';
  public $fields = array(
    'id' => array('type' => 'string', 'null' => false,
                  'length' => 36, 'key' => 'primary'),
    'ratings' => array('type' => 'integer[]', 'null' => true),
    'indexes' => array(
      'PRIMARY' => array('unique' => true, 'column' => 'id')
    ),
  );
  public $records = array(
    array(
      'id' => '0b07392c-d691-11e2-805f-080027347923',
      'ratings' => '{0,1,1,2,3,5,8,13,21,34}',
    ),
  );
}
```