Incoming is broken

[catamorphism]

rustdoctest tests segfault. Whatever commit introduced the problem, it wasn't one of the last 20 that show up on the buildbot console.

[catamorphism]

Narrowed down the problem to the call to vec::filter in prune_private_pass.rs. When I changed it to filtered, the problem went away. I'll file a separate bug for that. In the meantime, fixed in 0c05a6c