ICE from regions (Cannot encode region variables)

[thestinger]

I'll try cutting this down to a small test case later, but for now here are some in my TreeMap implementation (commented out):

• https://github.com/thestinger/rust/blob/f94da6e7d7e304204d10bcd4100b829f1ddd0ca0/src/libstd/treemap.rs#L51
• https://github.com/thestinger/rust/blob/f94da6e7d7e304204d10bcd4100b829f1ddd0ca0/src/libstd/treemap.rs#L673
• https://github.com/thestinger/rust/blob/f94da6e7d7e304204d10bcd4100b829f1ddd0ca0/src/libstd/treemap.rs#L683

[catamorphism]

Closing as per 3f7c74d -- reopen if I'm wrong!