Regression reports stable-2015-09-17 vs. beta-2015-10-02/nightly-10-06

Awesome! Thank you for doing the analysis @Eljay @eefriedman.

The cuckoofilter breakage was because of a bug that allowed it to import in a use list an unstable feature, which is fixed by https://github.com/rust-lang/rust/pull/28364