Improve shootout-reverse-complement
ignore-android
Make UdpStream block until the next non-empty msg.
Deprecate UdpStream
auto merge of #18143 : mahkoh/rust/reverse_complement, r=alexcrichton

Lots of unsafe code and lots of branches removed. Also multithreaded.

Rust old: 1.208 seconds
Rust new: 0.761 seconds
C: 0.632 seconds
auto merge of #18130 : mahkoh/rust/udp, r=alexcrichton

Closes #18111

Note that the non-empty part doesn't matter right now because of #18129.
Show a note when closure field is called as method

Closes https://github.com/rust-lang/rust/issues/18343
Add test for issue 18343