Change magic Nasal reftag to encode a quiet NaN (qNaN) instead of a
signaling NaN (sNaN), since sNaNs cannot pass cleanly through an FPU
(an sNaN is always converted to a qNaN, even by simple FPU load/store
instructions). gcc 4.5.x uses float load/store operations more
aggressively to move our 64bit Nasal variables (naRef) around.
Signed-off-by: Andy Ross