Set up framework for generic sets.
Added tests for lists as sets.
Generic implementation of sets that gets past bootstrapping phase.
Fixed a bug causing set/c to diverge.
Fixed treatment of lists as sets, and base case of case-lambdas.
Allow set-count to overcount for lists.
Disallow impersonators for set element contracts.
Fixed flat set contracts.
Fixed set/c to create a chaperone contract.