DSL :needs and :products numbers are off

[Vaguery]

There needs to be some adjustment made to push.instructions.core/needs-of-dsl-step and products-of-dsl-step. The 0 values are no longer necessary (although I suppose there should be checks on push-onto that automatically produce an empty stack if one is missing.

But more generally, it needs to differentiate between the need of a stack being present at all, and the need of things to be consumed.

[Vaguery]

partly fixed in 8d3cf00

need to make sure 0 values are read correctly in both directions

[Vaguery]

fixed in b56905f

[Vaguery]

this still fails to capture effects of stack-changing-steps

[Vaguery]

This is worse now that I've changed return values to go to :exec

[Vaguery]

Affected by #175