fixed invoice subtotal calculation failure, fixed cod fee including tax on pdf invoice

Hi, 

you've deleted my fix within a commit.

Please see information from last pull request:
https://github.com/PHOENIX-MEDIA/Magento-CashOnDelivery/pull/1

I've adapted the fix to work with the latest version of your module.

In addition I've changed the cod fee in invoice pdf info box. Now the cod fee is displayed including tax if selected in admin.

Best regards,

schnere