[plt-dev] phase for unbound identifiers

Could the error message for unbound identifiers always give the phase? 
As a corollary I dislike the name 'transformer environment'.

So instead of:
    compile: unbound identifier in module (transformer environment) in: take
-->
    compile: unbound identifier in module (phase 1) in: take

And in phase 2 I don't get any special indication at all (like 
'transformer environment').

    compile: unbound identifier in module in: take
-->
    compile: unbound identifier in module (phase 2) in: take

Maybe 'phase 0' could be elided during that phase since its the most 
common thing and people probably don't want to see it.