detect exactly equivalent intersection types for #596
eliminate supertypes with incorrect variance from model 'cos they can
result in nontermination
mention the equivalences that result from PII
simplify last commit for #596
minor
better fix, more complete fix for #596
disallow recursion from within intersection in supertype
fix npe for non-wellformed satisfies
extra test
additional test
squash npe
same treatment for union types for #596
update tests to take into account new restriction on unions in #596
whole new approach to dealing with circularities in type checker
recover nicer errors we had before with Emmanuel's code for detecting
circular inheritance
squash another nontermination case
much better error messages for circular type alias definitions
totally revise new circularity checking for much better error messages
new test
oops, fix test
fix description of doc archives for #189