Don't assert on union/isect flatten (#722)
Don't assert on union/isect flatten (#722)

It's possible to hit the flatten pass on types that have already
been flattened, for example when generating an anonymous type for
a lambda. Instead of asserting that the child count is 2, the
flatten step can be skipped if the child count is greater thant 2.
dipinhora/ponyc,Perelandric/ponyc,doublec/ponyc,kulibali/ponyc,ryanai3/ponyc,cquinn/ponyc,sgebbie/ponyc,ryanai3/ponyc,Praetonus/ponyc,Theodus/ponyc,mkfifo/ponyc,boemmels/ponyc,jupvfranco/ponyc,malthe/ponyc,jupvfranco/ponyc,mkfifo/ponyc,kulibali/ponyc,kulibali/ponyc,sgebbie/ponyc,Theodus/ponyc,malthe/ponyc,sgebbie/ponyc,jemc/ponyc,Praetonus/ponyc,Perelandric/ponyc,lukecheeseman/ponyta,Theodus/ponyc,boemmels/ponyc,malthe/ponyc,ponylang/ponyc,malthe/ponyc,Theodus/ponyc,boemmels/ponyc,Praetonus/ponyc,ryanai3/ponyc,jemc/ponyc,boemmels/ponyc,CausalityLtd/ponyc,dipinhora/ponyc,dipinhora/ponyc,Perelandric/ponyc,Praetonus/ponyc,CausalityLtd/ponyc,ponylang/ponyc,cquinn/ponyc,Perelandric/ponyc,sgebbie/ponyc,ponylang/ponyc,lukecheeseman/ponyta,sgebbie/ponyc,mkfifo/ponyc,Perelandric/ponyc,boemmels/ponyc,CausalityLtd/ponyc,jupvfranco/ponyc,lukecheeseman/ponyta,doublec/ponyc,kulibali/ponyc,cquinn/ponyc,Theodus/ponyc,mkfifo/ponyc,doublec/ponyc,mkfifo/ponyc,jupvfranco/ponyc,cquinn/ponyc,jupvfranco/ponyc,jemc/ponyc