Get/SetThreadContext doesn't work

GetThreadContext and SetThreadContext don't work at all. They just cause a BSOD
from KeTrapFrameToContext/KeContextToTrapFrame (apparently because the
KeGetCurrentThread()->TrapFrame is a bad pointer)

This bug may not appear to happen with GetThreadContext, because of another bug.
NtGetContextThread doesn't actually put the context into the
GET_SET_CTX_CONTEXT, so that part of it is just stack junk, which may not have
any of the context flags set in the context parameter, so the trap frame never
gets accessed.