Coprocessor args must be evaluated

[porcuquine]

As noted in #397, coprocessor arguments are currently passed unevaluated to the coprocessor. This is a severe limitation that needs to be removed. There are several approaches that might work, but they will all require at least some circuit changes — so it may prove best to defer this until the circuit is derived from a description of evaluation. However, solving this is critical to coprocessor usability, so whether we can afford todo that depends on how soon the derived circuit is completed.

[arthurpaulino]

LEM solves this