Compatibility with Dsdata_NoState

https://github.com/dsdata/NoState uses Mage_Adminhtml_Block_Widget_Grid and reimplements most of the code from Mage_Adminhtml_Block_Customer_Grid.

See https://github.com/dsdata/NoState/blob/master/app/code/community/Dsdata/NoState/Block/Customer/Grid.php for their reasoning.

On a side note, type hinting in magento seems to be pointless due to the custom error handler in app/code/core/Mage/Core/functions.php. When developer mode is not activated no exceptions are thrown and execution continues, effectively disabling type hinting.