DPS/Payment Express Utilities should be static functions

My logs are full of the following

[code][13-Feb-2014 19:59:21 UTC] PHP Strict Standards: Non-static method CRM_Core_Payment_PaymentExpressUtils::_xmlElement() should not be called statically in /sites/all/modules/civicrm/CRM/Core/Payment/PaymentExpressIPN.php on line 303 [/code]

This is due to the CRM_Core_Payment_PaymentExpressUtils class functions all being called statically, but not defined as such.

I have attached a patch to fix this - with the Utils functions now all defined as static - and proper (2 space) indentation applied. Hopefully this matches the style guide!