Panicking tasks should abort process if not handled

RFC for issue opened here: https://github.com/rust-lang/rust/issues/19610

Rust does not fully poison (see my example program, which uses shared memory, panics a task, and keeps on "running"). Nor does lack of poisoning make anything memory unsafe if it is only using safe constructs. It may introduce logic errors, and make writing unsafe code harder, sure. 

All I'm saying is that poisoning is not a sufficient remedy for the silent ignoring of panics. (And as a side note, poisoning should allow some way to opt out, so I can use a mutex with possibly-crashing tasks, like a webserver running user code, without having to write my own non-poisoning mutex. But, separate issue.)