[Yhc] AMD64 port complete (hopefully)

Tom, I have spotted the bug that was crashing the GC on AMD64 and now YHC seems to run stable on that platform. I'm sending the patches that darcs found missing in the official yhc-devel repo. I can't crash yhi anymore. It ran fine on Queens 4x4 test with QUITE_PARANOID turned on and heap size tuned to force garbage collection cycles. I think you can proclaim YHC ported to Linux/AMD64;) Or do you have ideas of other tests to run? Michal