Fix 386 structs to make test.go build and run

Hey Scott. I'm not even sure if Go-SDL2 is still being supported, or even the basis for different structs between 386 and Amd64 (I'm not very familiar with Go or SDL, screwing around with gaming libraries is just a hobby) but I managed to fix the parts that were causing test.go to fail to build on my machine (32 bit Ubuntu 13.04 installed on a  64 bit MBP).

To me it looked like most of the 386's structs were just out of sync with the changes to the Amd64 structs, so I assumed that there wasn't any special optimization decisions, at least where the code was breaking. I hesitated to do drastic changes because I didn't understand the need for these structs to be different in the first place.