Pab/devel - conditional exports

Lots of stuff here, largely fallout from noticing that A(T: with): with { x: % } == add { if A has B then x: % == ... }
was accepted when it shouldn't be. 

 Along the way also fixed:
- algebra/aldor/foamlib conditional mixups
  - normalize$FractionBy X, where X isn't a GCD domain now throws an error; not sure what the correct implementation is
- prime?(z)$F matches prime?(z) for the purposes of conditional expressions
- the form 'with { x: % }' now works properly across file boundaries.
- "and" in conditional exports was very broken

This does not yet completely fix #87, but gets close.