`cargo test` doesn't capture print from threads

[kpcyrd]

I ran the tests for one of my crates that uses threads in its example code. I've noticed it printed some lines to stdout, even though --nocapture wasn't set, but not all of them. It appears that text printed from new threads are not correctly captured, I think this is not intended.

running 2 tests
request: 123
test tests::readme ... ok
test tests::single_requester ... ok

[Mark-Simulacrum]

You're correct, this should be filed on rust-lang/rust (closing in favor of rust-lang/rust#42474).