Add some more prefix tests for the vfpu

Currently fails, but not as bad with a pull I'm about to send.

Unless I did something wrong, it seems like it considers `-NAN + -1/3 = +NAN`.  I'm not sure how important that is, I could remove it.

I also commented out some tests that show what happens when you use out-of-bounds swizzles.  Not sure how accurate we want to get on some of those since I really doubt games will do that (but you never know...)  And I'd written, but then removed some more involved vscl tests using vprfxt, which just have bizarre results.

-[Unknown]