Rename UnusedArgs to Erasure.
Remove export of traceUnused.
Simplify unused arg search.
Cleanup and purification in Erasure.hs.
More purification.
Simplification with pattern guards.
findUsed stub written.
Make ProjCase take exactly one alternative.   (TODO: is this safe?)
Intercommit. (Deeper usage analysis.)
Ctor usage analysis roughly complete.
Intercommit.
Another intercommit.
Reapply 08779298ce2e95b3e16a5a3e5d9c0cf3936d0507 from master.
Intercommit.
Redefine dep analysis data structures.
getDeps extended.
Intercommit.
getDepsTerm somehow implemented.
Improved dep pretty-printing.
getDepsTerm covers all cases.