Turn eval into evali

[jmaessen]

This is based on the observation that two things can happen in eval:

• The stack is clear, in which case the value in n is a direct reference to the WHNF of the original argument
• The stack is not clear, in which case the top of stack is an AP representing the argument without indirections.

In either case there's no need to push / pop it again and go chasing after indirections.

This represents a small time savings of about .2s on bootstrap, see https://docs.google.com/spreadsheets/d/1Tw6LLwTEU0VxdWcf_ZUF1_T9KlchpNEFXKNiAarxd4I which shows data from 10 interleaved after/before runs plus some statistically bootstrapped averages with histograms showing limited overlap.

[augustss]

Excellent observation.