Gateways that use TE2 functions don't check for TE2

[JeffPyeBrook]

the paypal digital goods and express checkout gateways use the TE2 function _wpsc_get_current_controller_name(), but don't check to see if TE2 is loaded

Two issues....

1. It is unclear if the gateways are dependent on TE2
2. If the gateways are dependent on TE2, they should check for TE2 being active before loading

[JustinSainton]

A couple notes on this:

• All new payment gateways will have implicit support for TeV2, and will have to explicitly declare support for tev1, which will be technically "deprecated" as of 4.0.
• The places these gateways use that function are hooked into Tev2 are using hooks that are specific to that theme engine.
• That all said, the main todo here is to decide whether or not these gateways should support tev1, to what degree if so, and decide what needs to be done to complete that.

That can all be done outside of 4.0.