Fails Pixley^3

[cpressey]

As mentioned in Pixley's test.sh, running the Pixley test suite on the (Pixley reference interpreter)^3 fails under minischeme (although ISTR it is only one test which fails.) It's strange that this should only fail at Pixley^3 and not at Pixley^2 and suggests it is some obscure limitation inside miniscm. (Perhaps the memory has been exceeded somehow, without a warning or other explicit symptom.)