Payment driver for Securepay gateway

[ae]

I have created a Payment driver for securepay. I've tried to keep it as close to the examples as possible, however there were no secure socket examples in there.

We are currently using this in production, however one thing which we have done differently locally (but not included in the attached files) is implement a return array for the process method. The return array contains error messages and codes as well as (obviously) success or failure. This type of functionality is a feature request already ticket:522

Assigning this to zombor - I hope this is the right person :)
Oh and the code is based on the current trunk changeset:2833