[libogc] structs Vector and Quaternion should be renamed

[punto]

On the gu library, the structs 'Vector' and 'Quaternion' pollute the namespace, should be renamed to something like 'guVector' and 'guQuaternion' (just a mass replace on gu.h and gu.c worked for me)

also, gx.h includes gu.h, shouldn't be the other way around? (you should be able to include just gx if you don't use the stuff from gu)