Fix ffi example (#949)
Fix ffi example (#949)

Was broken a while back. Reading a field on a class through
an iso (like Inner here on Outer) results in it being a tag.
Aka doesn't work. Explicitly make Outer a ref rather than an iso.
dipinhora/ponyc,boemmels/ponyc,jemc/ponyc,boemmels/ponyc,ponylang/ponyc,lukecheeseman/ponyta,Theodus/ponyc,mkfifo/ponyc,Theodus/ponyc,boemmels/ponyc,CausalityLtd/ponyc,Praetonus/ponyc,malthe/ponyc,dipinhora/ponyc,sgebbie/ponyc,Praetonus/ponyc,jemc/ponyc,ponylang/ponyc,jupvfranco/ponyc,kulibali/ponyc,CausalityLtd/ponyc,kulibali/ponyc,Theodus/ponyc,kulibali/ponyc,dipinhora/ponyc,malthe/ponyc,jupvfranco/ponyc,Praetonus/ponyc,ponylang/ponyc,Perelandric/ponyc,Praetonus/ponyc,Perelandric/ponyc,sgebbie/ponyc,sgebbie/ponyc,sgebbie/ponyc,Perelandric/ponyc,cquinn/ponyc,mkfifo/ponyc,boemmels/ponyc,kulibali/ponyc,mkfifo/ponyc,Theodus/ponyc,cquinn/ponyc,jupvfranco/ponyc,malthe/ponyc,lukecheeseman/ponyta,Perelandric/ponyc,Theodus/ponyc,Perelandric/ponyc,cquinn/ponyc,jupvfranco/ponyc,jemc/ponyc,CausalityLtd/ponyc,boemmels/ponyc,mkfifo/ponyc,cquinn/ponyc,jupvfranco/ponyc,lukecheeseman/ponyta,malthe/ponyc,mkfifo/ponyc,sgebbie/ponyc