Bug: garbage collector will erase floating values

[VictorTaelin]

Example:

(Hold a b) = (λx(b) a)
(Copy v f) = (f v v)
Main       = (Hold (Copy 5 λ$aλ$b(0)) $a)

On HVM1, it outputs <era>. The correct answer (as printed on Bend) is 5.