Work-around 'static bound requirement in io::with_bytes_reader (note: does not fix #5723, interface still unsafe)
Infer default static/Owned bounds for unbounded heap fns/traits (#7264)
Looser restrictions on what can be captured in unbounded traits.
Make closure contents call out to trait_contents.
Looser restrictions on what can be captured in unbounded heap closures.
Fix pretty-printing for bounded closures. Close #7333.