Fix/remove some half-baked stuff I left in the prekern:
- Page-align the idt store, to be extra sure.
- Remove unneeded prototypes.
- Drop the TSS, we don't care and aren't even using it.
- Initialize %ss with a default value.
- Fix three exception handlers, no need to push an error code.
No actual impact, because these things are used only when returning from
exceptions received in the prekern; these exceptions are not supposed to
be ever received, never are, and if they were we wouldn't return anyway.
UnifiedSplitRaw
